
Dry Rot 

IN 

Factory Timbers 



1922 



INSPECTION DEPARTMENT 

Associated Factory 

Mutual Fire Insurance Companies 

Port Hill Square 
184 High Street, Boston, Mass. 



Since the first edition of this pamphlet was published 
there have been many changes in the problem of secur - 
ing reliable lumber for factory construction. During the 
war it was impossible to buy the selected high-grade 
F. M. Southern pine recommended in the first edition. 
Whether it will be possible to secure this dense resinous 
material at a reasonable price in the future is problem - 
atical. Douglas fir from the Pacific coast is coming into 
the Eastern market in increasing quantities and has many 
desirable characteristics which commend it for factory 
construction. Its usefulness will be greatly increased if 
it is given a light antiseptic treatment at the saw-mill to 
keep fungus out of it on its long journey as well as in the 
lumber yard, where it may rem^ain for some time before 
it is put into its final position in the factory building. 
Treatment at the saw-mill of all structural timbers is de- 
sirable as most of the destructive infection in heavy tim- 
ber is contracted before it is put into the structure. 



Dry Rot 

IN 

Factory Timbers 



1 922 



INSPECTION DEPARTMENT 

Associated Factory 

Mutual Fire Insurance Companies 

Port Hill Square 
184 High Street, Boston, Mass. 






Copyright, 1915, \>y 
C. H. Phinney, Trustee. 

Copyright, 1922, by 
H. O Lacount, Trustee. 




M -3 1922 

C1A676943 



m 



^ ,CC\ 



^- - CONTENTS 

-) (See Index in Back of Pamphlet) page 

Abstract 2 

Recent Progress . 4 

Extent of Destruction 5 

Roofs Are the Source of Greatest Loss from Rotting .... 8 

Dry Rot and Fire Hazard 9 

Increased CombustibiHty of Wood Affected by Dry Rot ... 11 

Suggestions for Examining an Infected Mill 12 

How Wood Rots 17 

Common Timber-Destroying Fungi 18 

Rapid Progress of Dry Rot 27 

Effect of Humidity on the Progress of Rot 28 

Dry Rot and Damp Rot 32 

Local Differences in Exposure to Moisture t^t, 

Extremes of Wetness and Dryness Both Prevent Rot .... 36 

How the Dry-Rot Disease is Spread 41 

Heat and Drying are Useful in Stopping Rot 42 

Holes in Columns and Double Beams Will Not Prevent Rot . 45 

Slow-Burning Construction 47 

Roof Design 50 

Arrangement of Heating Pipes 63 

Special Humidification of Cotton Factories . . . ^ 71 

Available Lumber and Insulating Materials 73 

Varieties of Timbers Available . . . ; 74 

Cheapness as an Index of Quality 75 

Common Varieties of Southern Pine 75 

Rosin as a Cause of Resistance of Wood to Fungi 83 

Density as an Index of Strength 87 

Specifications for Structural Timber 90 

Interstate Rules for Grading Lumber 93 

Specifications Suggested for a Special Grade of Longleaf Pine 

for Use in Mutual Factories 95 

Chemical Treatment to Prevent Rot 99 

A Use for Creosoted Lumber in Insulating Roofs of Moist 

Factories 112 

Penetration of Antiseptics 114 

Cost of Timber Treating . 115 

Summary 116 



INSPECTION DEPARTMENT 

Associated Factory 

Mutual Fire Insurance Companies 

Fort Hill Square 
184 High Street, Boston, Mass. 



March 15, 1922. 



DRY ROT 

IN 

FACTORY TIMBERS. 



The interest of the Factory Mutual Insurance Com- 
panies in Dry Rot of Timbers is threefold. 

FIRST: They have for fifty years been sponsors for so- 
called slow burning or mill construction. The economy 
and integrity of this excellent type of building is threat- 
ened by the remarkable increase in the prevalence of dry 
rot during the past few years. 

SECOND : Wood infected by dry rot ignites more easily 
than sound wood and mill timbers with rotted ends fall 
more quickly under fire. 

THIRD: The officers and engineers of these companies 
believe that the dangers of dry rot can be largely elimi- 
nated, with the consequent saving of many thousands of 
dollars to Mutual members. 

No. 32. 

3rd Edition. 

3000-3-22 



BRIEF ABSTRACT OF FOLLOWING PAGES. 

1. More than one hundred cases of dry rot, of greater or less 
magnitude, have been brought to the attention of the ]Mutual 
Companies within the past ten years. Millions of feet of lumber 
were involved, and, in some of the worst cases, the safety of im- 
portant structures was menaced. There were undoubtedly 
many other cases which have not been reported. The direct 
money loss to Mutual members from this source is undoubtedly 
many thousand dollars each yea,T in addition to the increased 
fire and life hazard from loss of strength and greater combusti- 
bility of rotting structural timbers. 

2. The varieties of fungi causing this destruction of factories 
are apparently few, and, while their habits and requirements 
are not well known, it is evident that the supply of moisture 
and the temperature are important controlling factors. 

3. Each variety of timber has its own peculiar fungus de- 
stroyers, and, as the number of varieties of timber practically 
available for mill construction is limited, the problem is some- 
what further simplified and resolves itself into the selection of 
timber with the greatest natural resistance to fungi practically 
attainable, and seeing that this is dry and free from dangerous 
living fungi when placed in the structure. 

4. In most cases, it is well worth the cost to thoroughly 

heat the building by use of its heating system as soon as possi- 
ble after it is completed. This will hasten the drying and kill 
surface growths of dangerous dry-rot fungi. This may fill 
all requirements in buildings of dry occupancy. 

5. The moist atmosphere present in such processes of manufac- 
ture as paper making and cotton weaving, introduces conditions 
which probably no variety of wood now practicalh' obtainable 
can withstand continuous!}' without having its natural resist- 
ance to fungi reinforced by artificial antiseptic treatment. 

6. Timber of uniformly high natural resistance to fungi is 
difiicult, if not impossible, to obtain by grading methods now in 
general use. The dense resinous longleaf pine from the butts of 
trees, which has been used in the past, has proved satisfactory. 
The present supply of so-called " Commercial longleaf pine," 
comprising all varieties of Southern pine (Xorth Carolina, 



shortleaf, loblolly and Cuban, mixed indiscriminately with true 
longleaf), is proving far less reliable than the supply of former 
years, and thus far no standard specifications have been 
adopted by means of w^hich the purchaser can assure him- 
self of the reliability of the lumber delivered. 

7. The percentages of rosin and the density are undoubtedly 
valuable indices of durability and strength. The rosin test is 
somewhat cumbersome to apply and is not recognized by the 
lumber trade. The density is roughly covered in the " Growth 
ring " or " Grain band rule " adopted by several lumber asso- 
ciations. 

8. It is probable that a close observer, who has had con- 
siderable experience with Southern pine, could select resinous 
dense wood with considerable certainty, and it is doubtless 
worth while for a large user of Southern pine to employ such a 
man as buyer at the saw-mills. It is, of course, necessary to pay 
a premium for such selected timber, but it is well worth it, since 
a free gift of unreliable w^ood in an important structure 
would be expensive. 

This close examination is impracticable for the small or occa- 
sional purchaser, and to such the only course that can be at 
present recommended is to buy heartwood timber of w^hich 
the density, as indicated by the grain bands, is sufficient 
to insure the required strength, and to give this a chem- 
ical treatment, if it is to be used in a moist location. 

9. The process of antiseptic treatment used should be selected 
w^ith reference to the amount of moisture to be present 
where used, a vacuum and pressure process with hot creosote 
being advisable for lumber in contact with the earth or tightly 
enclosed in a moist condition. Corrosive sublimate or sodium 
fluoride is serviceable where color or painting is an important 
consideration. 

Arrangement of heating coils and ventilation to keep the 
temperature of roof planks above the dew-point can greatly 
increase the life of a roof. 

Insulating material on the outside will increase the life of a 
new roof and may considerably prolong that of an old one which 
has started to rot. 

Heat insulation on roof drains, vent pipes or other metal pipes 
exposed to outside air, will prevent local rotting about such 



pipes b}' preventing loss of heat and therefore precipitation of 
moisture. 

Rotting in basements can more certainly be stopped by heat- 
ing than by ventilation alone. 

RECENT PROGRESS. 

Since the publication of the first edition of this pamphlet in 
December, 19 13, progress has been made towards assuring more 
reliable timber for mill construction. 

The problem divides itself into two parts: 

First, that of untreated timber, or the possibility of securing 
uniformly reliable timber at a permissible price, which possesses 
sufficient natural resistance so that unaided it can withstand 
fungus in the moist atmosphere found in many rooms in textile 
mills, or in paper mills. 

Second, that of timber treated antiseptically, or timber which 
can be had in suitable lengths and sizes, with sufficient strength 
for the required load, and which can be given the necessary re- 
sistance to fungus by chemical treatment. 

In the past, good quality longleaf pine has given satisfactory 
service without antiseptic treatment; but the present supply, 
which comprises much loblolly, shortleaf and poorer longleaf, is 
lacking in natural resistance. Therefore, in order to make sure 
of obtaining a grade of Southern pine which can be used safely 
without antiseptic treatment, the present system of grading 
must be revolutionized, and based upon those physical and 
chemical properties which underlie strength and resistance to 
fungus rather than upon the vague botanical distinctions. It is 
doubtful whether it is practicable to do this at present owing to 
the scarcitv of high-grade timber. 



EXTENT OF THE DESTRUCTION. 

The loss to Mutual mills from rotting timber is many 
thousands of dollars a year. It is not possible to state the 
amount with even approximate accuracy. The following photo- 
graphs will convey some idea of the character and extent of the 
destruction in a few cases. 




Fig. I. 

Part of 239,000 feet of spruce roof plank and hemlock floor beams removed 
from a Massachusetts cotton factory due to rotting in from two to four- 
teen years. 




Fig. 2. 
Seventeen 12" x 16" Southern pine beams rotted and removed after two years' 
service in a cotton factory in Connecticut. 




Fig. 3. 

Part of 750 8" X iS" beams removed from a new factor." in Montreal, after 
onlv three vears" 5er\'ice. because rendered unsafe bv decav. 




Fig. 4. 

Tin clad fire door of -white pine, badlj- rotted onh* three j-ears after it was 
installed in a ^Massachusetts cotton factor>% 






Fig. 5. 

Hemlock beam, rotted and crushed under a light load, after two years' 

service in a moist basement. The adjacent longleaf pine column is still 

serviceable after fourteen years. 




Fig. 6. 

Rotted column crushed in an Ohio paper mill. The timber is loblolly pine. 
The rotting was started by ^the timber being soaked by a flood. 



ROOFS ARE THE SOURCE OF GREATEST 
LOSS FROM ROTTING. 

^lore than fifty rotted roofs have been studied within the past 
five years. Part of these have been kept under observation for 
a period of two or three years. The sheathing was removed 
from one Xew Bedford weave shed five 3'ears ago exposing great 
numbers of fungus plants which have been normall}- growing 
and frmting since, giving an exceptional opportunity to deter- 
mine with certainty the varieties of fungus responsible for the 
destruction as well as their methods of growth, seasons of fruit- 
ing and moisture requirements. In this stud}' Mr. C. J. Hum- 
phrey, pathologist of the United States Forest Products Labora- 
tories and ]Mr. R. J. Blair, pathologist of the Canadian Forest 
Products Laboratories, have co-operated and for the identifica- 
tion of the fungi mentioned in the following pages we are in- 
debted to these gentlemen. Studies which give promise of valu- 
able practical results are in progress at both of the above men- 
tioned laboratories. 

Steam pipes have been rearranged experimentally in parts of 
three large weave sheds and another has been entirely repiped. 
Three roofs have been insulated on the outside with a \-iew to 
stopping rot which was progressing rapidly in them and thereby 
sa\4ng the old roof. In one large weave shed with a sheathed 
roof in which rot has started the space under the sheathing has 
been vented to the outside air in order to study the efficiency of 
this method of removing the moisture. F. AI. Grade Southern 
pine plank has been used on one new roof, California redwood 
has been used in replacing one rotted roof and Kyanized spruce 
has been used in replacing several others. 

These experiments have been started as a result of observa- 
tions on the beneficial effects of similar arrangements which 
have been in service in parts of existing buildings for long periods 
of time. It is evident that if the results of experience in existing 
factories covering many years can be gotten together an im- 
portant advance can be made in the art of construction. 

The average life of roofs of highly humidified wea\4ng mills, 
poorly ventilated paper mill machine rooms and can rooms of 
bleacheries is twelve years. This life can certainly be increased 
to twent}' or more 3-ears by careful attention to the location cf 



heating coils, arrangement of the ventilation and suitable 
insulation. 

The present high prices of labor and lumber make it more 
important than it was formerly, to so design a roof that it 
will not rapidly deteriorate, as it is far more expensive to re- 
place it. 

DRY ROT AND FIRE HAZARD. 

Partly rotten wood ignites much more easily than 
sound wood. 

Dry rot in factory timbers is of importance not only from the 
cost of replacement and the danger of collapse, but because it 
increases the fire hazard. The increased combustibility of rotted 
fence posts and stumps is familiar to many casual observers. 
The collapse of the Gledhill Wall Paper Factory of New York, 
after a small fire,^ presented an illustration of this hazard. 




Fig. 7. 

Shows ends of mill beams completely destroyed although the beams them- 
selves are not deeply burned. 



1 Engineering News. Vol. LXII, 1909, p. 620. 



10 





Fig. 8. 
Shows two sections of 14" x 16" white pine beams, with rotted centers, 
which were recenth" removed from one of the older cotton mills. When 
lighted with a match, they continued to burn until all of the rotted wood 

was consumed. 




Fig. 9. 

Floor beams described above after the ignited rot had burned awaj", th: 
fire going out of itself when it reached the sound wood. 



11 



THE INCREASED COMBUSTIBILITY OF WOOD 
AFFECTED BY DRY ROT. 

The ignition point of rotted wood has been shown to be lower 
than that of sound wood.^ 

Under favorable conditions, large pieces will ignite at a tem- 
perature of 290° F., or even lower. 

The Mutual Companies have no definite records of increased 
losses from this source, owing, doubtless, to the efficiency of the 
complete automatic fire protection in Mutual risks, by means of 
which the fire is ordinarily extinguished before the fire-resistant 
qualities of the construction are severely tried. 



1 Henry B. Hill, Proceedings of the American Academy of Arts & Sciences, 
Vol. XXn, 1886, p. 482. 



12 



SUGGESTIONS FOR EXAMINING AN INFECTED MILL. 

In examining a mill affected ^^ith dry rot. it is especially de- 
sirable to determine how far the rot has extended, whether it is 
still alive and whether it is of a variety which goes into a resting 
state, and may, therefore, be revived at any time when the condi- 
tions of moisture become favorable; also, whether it is a variety 
which may be destroyed by moderate heating or drying. 

The extent of the rotting can generally be estimated approxi- 
mately by boring test holes into the beams and columns at 
frequent intervals. If the material is badly rotted, the chips 
brought out will be in the form of a brown powder or mud, accord- 
ing as the wood is dry or wet. Sometimes, where the rot has not 
progressed so far as to entirely destroy the structure of the wood, 
the chips are browner than the sound wood and more brittle. 

A useful indication of the presence of "rotted wood in a ceiUng 
is the brown extractive Kquid which runs down the beams and 
leaves brown streaks. The number and location of these streaks 
indicates the relative extent and location of the rotting, as 
shown in the following photograph. Figure lo. 



"wm^ ^-"-^ 


■ \ 
\ 

\ - ■ 


-ii 










Fig. io. 
Dark lines of extractive matter on the beams from the rotted planks can be 

used as an index of the internal rotting. 



13 

A matter of interest in this case is that this part of the roof 
which is evidently more rotted than the remainder, is only three 
years old while the older part which is still in service is fifteen 
years old, showing that replacing a rotted roof with new planks 
will not necessarily assure as great a life in the new roof as was 
shown by the old one; in other words, the kind of lumber and the 
design of the roof have a greater influence on its life than its age. 

In order to demonstrate the usefulness of this indication a 
plan of a weave-shed ceiling was made and marks of equal size 
were attached to the lines representing the beams wherever the 
brown lines appeared on the beams. This plan is shown in 
Figure ii. The influence of the loss of heat through ventilators 





•■'" .' . 






• • a • 

' ' ' V *„^. 


' '■' 'm ■■■ "''■ "'"a . " «/ 


■i. " • 


m. Ur^l.-, . ' .• ' • •' " , 

■ a a 
t ,'M -* ♦ , « " .' ■,■•#» 


'3- * ■ ** < f *( «• , 






a ' a a • 






r*. - ♦ " " ^ ' "' " 


" ....... 










■■"■■ ■ 


\ , , . . , ' 


■ . . ' " ■..'',•' ,?, • 


*."- '^ ■ « K 


. , , ■ , " • 









.. * w J 






Fig. II. 
Short lines on the lines representing the roof beams show the number and 
location of streaks of extractive matter on weave-shed roof beams and there- 
fore the distribution of the rot. The black squares represent ventilators. 
Note the increased rotting near the ventilators, also the decrease near the 
outside walls where there are additional heating coils. 



14 



and the heat locally added by the extra steam pipes around the 
sides of the room is apparent. 

Hammering on beams or columns with the round end 
of a machinist's hammer is sometimes useful where the wood 
is in an advanced state of decay. In some cases, where this 
test has been applied, the outer shell of apparently sound beams 
has been broken through, showing the entire destruction of the 
interior. See Figure 12. The rotting of roof planks is generally 




Fig. 12. 

12" X 14" beam taken from a factory fifty 3'ears old. Warning of the con- 
dition of this beam was given bj- the settling of the column which was 
supported by it and in turn supported three stories of the factory. 



much worse above the beams than in the middle of the bay, 
and, in some cases, planks which appear sound on the exposed 
surface will be found rotted above the beams so that a knife 
blade can be pushed entirely through them. It is from this 
source that the brown extractive matter mentioned above 
chiefly originates. 

To determine whether the rot is still alive is a more com- 
plicated matter. If it is growing vigorously on the surface of 
the wood, the fresh growth of lacelike plants gives conclusive 
evidence, but the more frequent condition is where the 



15 



fungus is growing inside the wood with no outward mani- 
festation. In this case, a strong indication of living fungus is 
the moist appearance of a freshly cut section. In some cases, 
moist spots will remain for several days on such a section when 
left in a comparatively dry room. The most reliable test, how- 
ever, is to cut a large number of blocks about 23^" cube from 
the wood at the point where the rot just ceases to be apparent 
by the brown color, so that a part of each block is brown and a 
part of it has the appearance of sound wood. These should be 
placed in fruit jars and soaked in water containing 2% of citric 
or tartaric acid for about six hours, then the water should be 
poured off and the jars covered and left at a temperature of 
about 75° F. for two or three weeks. If long threadlike growths, 
such as those shown in Figure 13, appear on any specimens, the 





Fig. 13. 

Sterile rot plants as commonly seen. These plants were cultivated 

on small blocks in fruit jars. Scale one-half natural size. 



fungus is doubtless alive and of a suspicious variety. Micro- 
scopic molds of various colors not infrequently appear on such 
cultures, but they do not indicate a wood-destroying fungus. 

The culture blocks will not only show fungus in active 
growth, but also living fungus in a resting state. This is 
the only sure way in which fungus in this treacherous state can 
be discovered. Microscopic examination of sections would indi- 
cate whether they contained the bulblike formations shown in 



16 

Figure 20. indicating the resting state, but would not show 
whether or not they were alive. It is very rare indeed that 
fruiting plants, whether of the dry rot or other varieties, are 
found on structural timbers above the basement. Therefore, 
spores, the normal reproductive body, are probably not common 
causes of perpetuating the disease in factories. Such fruiting 
plants are moreover very easily seen and identified unless they 
are growing inside of hollow partitions or in concealed basements, 
as sometimes occurs. 

Such culture tests require so much time and such compli- 
cated methods that they can rarely be made of much practical 
value except in rare cases when it may be desirable to deter- 
mine whether rotten wood found in a structure is of recent 
origin or the result of an old fungus which may have long since 
ceased active growth. In such cases the results must be cau- 
tiously interpreted, due to the power of many of the fungi already 
mentioned of going into a resting state in which they may re- 
main dormant for years. 

The governing factors in fungus activit}", as in all other living 
organisms, is food and water, or water-attracting materials. 
Fungus will grow on sap wood and stop sharpl}- at the heart. 
It will grow near a refrigerator or cold-water pipe where the water 
required by the plant is precipitated out of the atmosphere by 
the low temperature in the same manner that an ice-water pitcher 
"sweats" on a summer day. 

The control of the local water supply by heat and ventilation is 
generally by far the most practicable way to arrest the rotting. 

Certain kinds of dry-rot fungi can sometimes be arrested 
by heating, while with other varieties this is not effective. 
Where there are no fruiting plants, the only practicable course 
is to judge, from the location of the rotted lumber, the probable 
sensitiveness to heat of the fungus causing the destruction. 
For example, a rotted roof plank in a paper mill or weaving 
mill, with the normal temperature from 80° F. to 100° F. at the 
roof, and frequentl}" in summer higher than this, would not be 
expected to contain a variety of fungus which could be killed by 
heating to 115° F., while with rot discovered in the beams or 
columns of a moderately dry new mill, with an average tempera- 
ture of 70° to 80°, heating would be worth a trial without fur- 
ther evidence as to the exact variety of fungus present. If fruit- 
ing plants are found, which rarely occurs, the plan of procedure 
may be somewhat simplified. 



17 

HOW WOOD ROTS. 

Rot in wood was originally supposed to be a chemical action 
similar to rusting of iron, and the delicate lacelike plants, tough 
brackets, or brown leathery growths, were supposed to be at- 
tracted by the decayed wood rather than being the cause of the 
rotting. About 1870, it was shown by Hartig and others in 
Europe that fungi were the cause of rot instead of a result of it. 
The chemistry of the rotting process is not well known at the 
present time. It is probable that there is some chemical action 
in addition to the life progress of the fungus through the wood 
cells. It is noted in blocks of sound wood, in which fungus has 
been cultivated, that when the fungus is freshly removed 
from the moist wood, it has the appearance of being as 
bright and sound as ever; but, after being left in a dry at- 
mosphere for a time, the wood shrinks and forms the charac- 
teristic brown, cracked and powdery material which is familiar 
as rotted wood. 

Without doubt, the fungus ceases to make any vital progress 
very soon after the drying commences, and the final browning 
and powdering is brought about by oxidation by the air, assisted 
by certain organic enzymes, either already present in the wood 
cells or formed by the activity of the fungus. A phenomenon 
which supports this theory is that the plants of certain wood- 
destroying fungi when folded in a piece of white paper discolor 
it, changing it to a brown substance, probably an oxy-cellulose, 
leaving a fairly well defined impression of themselves upon the 
paper. They will also form a developable image on a photo- 
graphic plate in the dark. 

It is customary in many lumber yards, particularly where 
Southern pine lumber is sold, to pass the planks and timber 
through a planer immediately before delivery. This not only 
smooths the material, but removes all fungus plants and leaves 
a bright surface which can be easily mistaken for sound 
wood, if it is used before drying has brought out the brown 
spots which are recognized as rotten wood. 

Most of the worst cases of rotting of heavy factory timbers 
have been the result of fungus which was actively growing deep 
in the wood in the lumber yard before it was built into the struc- 
ture. This is particularly true of the dry-rot fungus which grows 
rapidly but is rarely found above the basement of any but the 
most moist factories. This is doubtless due to its sensitiveness 
to moderately high temperatures. 



18 



NAMES OF THE COMMON TIMBER-DESTROYING 

FUNGI. 
There are but few common or popular names for fungi, 

and the few there are, such as dry rot, punk, toadstools, etc., 
are exceedingly vague and indefinite. The Latin names are 
commonly used in scientific literature. Their use implies an 
exact identification which is rarely obtainable in rotting struc- 
tural timber. 

In this pamphlet, the words " dry rot " are used to signify 
broadly any of the structural timber-rotting fungi. The follow- 
ing photographs show fruiting plants of wood-rotting fungi 
most frequently met with in factories. 




Fig. 14. 

Merulius lachrymans, or dry rot, with fruit, on beam removed from cotton 

factory in Canada. Scale one-third natural size. 




Fig. 15. 

Merulius lachrymans growing on a Southern pine beam in the basement 

of a cotton storehouse in Rhode Island. Scale one-third natural size. 



19 




Fig. i6. 

Coniophora, with fruit, on a beam removed from a cotton factory in Canada. 

Scale one-third natural size. 




Fig. 17. 

Trametes serialis from basement of a Massachusetts cotton factory. 

full size. 



Scale 



20 




Fig. i8. 
Normal fruiting plant of Tranietes serialis growing in a weave-shed base- 
ment. This fungus has been found both in basements and on roofs, although 
rather more frequently in basements. Scale one-half size. 



The dry-rot disease is widely distributed in this country, 

but it has been more carefully investigated in Europe, especially 
in Germany. Forty dry-rot cases have been brought before the 
German courts within the last fifteen years. ^ 

In past years, little careful study has been given to the disease 
in this country, but the occasional cases recorded ^ indicate that 
it was more a question of the general use of material of sufficient 
natural resistance to withstand fungus under the condition of 
use than the absence of the disease. 

Fruiting fungi can be easily identified, but it is difficult 
or impossible to positively identify the young sterile grow- th. 

The chief use in identification is to help in determining 
the best curative measures to apply. For example, the 
Lenzites can stand high temperatures, nearly up to the boiling 
point of water,^ while the dry-rot family are killed at a compara- 
tively low temperature, W'hich peculiarity suggests a curative 
process to be explained later on, as knowledge of the life require- 
ments of the different fungi accumulates, exact identification will 
doubtless have more practical value. 

1 •' Hausschwammforschungen," Vol. II (1908) and Vol. V (1911). 
- Charles T. Main, "Notes on Mill Construction," p. 31. 
3 " Hausschwammforschungen," Vol. III. 



21 




Fig. 19. 
Fomes roseus, a common basement fungus on a hemlock beam in a moist 
basement of a Massachusetts cotton factory. Scale one-tenth natural size. 



In many cases, owing to the absence of fruiting plants, 
the particular kind of fungus causing the destruction can- 
not be determined. It is generally impossible to tell with any 
degree of certainty, from the appearance of the rotted wood, 
what fungus is responsible for the destruction. 

There is undoubtedly a difference in the microscopic appearance 
of the fungus plants in the wood cells, as can be seen from some 
of my photo-micrographs, reproduced in Figures 20, 21, and 22, 
but their peculiarities have not been much studied or described 
in the treatises available.^ 




Fig. 20. 

Coniophora in loblolly pine wood cells, magnified about 400 diameters. 
Section tangent to the tree. 



1 " Zersetzunsgerscheinungen des Holzes," Robert Hartig, 1878. 



22 




Fig. 21. 

Fungus passing through loblolly pine wood cells, probably Trameies se- 
rialis. Magnified about 400 diameters. Section tangent to the tree. 




Fig. 22. 
Ceratostomella pilifera, or blue sap pine fungus, in wood cells, 
about 400 diameters. Section tangent to_the tree. 



Magnified 



Three of four varieties of the wood-destroying fungi appear to 
be most active in the destruction of roofs. The true dry-rot 
fungus or Merulius lachrymans is not among these, doubtless 
owing to the fact that it cannot live at the high temperature to 
which roofs are commonly subjected. This fungus together with 
its frequent associate, the Coniophora cerebella, while very de- 
structive, generally confine their ravages to basements, bottoms 
of lumber piles and new buildings into which they have been 
introduced with the lumber. The varieties of fungus found in 
factory roofs fortunately have moisture requirements which 
limit the field of their ravages quite narrowly to the parts of the 
roof which are practically at the dew-point, slight variations in 
moisture and temperature favoring one or another variety. 



23 



The Lenzites shown in Figures 23, 24, and 25, which is the 
most common and destructive of the roof destroyers, can grow 
through a wider range of moisture than some of the others and 
can withstand a comparatively high temperature. 











Fig. 23. 

Lenzites trahia growing on the roof planks of a New Bedford weave shed. 

Lenzites trahia is one of the most common destroyers ot 
weave-shed roofs. It is rather greyer in color and has finer pores 
than the Lenzites sepiaria which is more common out of doors 
and is seal brown in color on top and yellowish on the under side 
containing the pores. 




Fig. 24. 

Lenzites sepiaria on'^spruce roof plank removed' from a Massachusetts 
cotton factory. Scale full size. _^Under side of the'plant showing the pores. 



24 




Fig. 25. 

Normal fruiting plants ol Lenzites sepiaria growing on Southen pine roof 
planks of a cotton weave shed after the sheathing had been removed 
for some time. Top of the plant. 



The Lentinus lepedius shown in Figures 26 and 27 which 
when fruiting normally looks very much like a common toad- 
stool is generally found in the more moist locations at the base 




Fig. 26. 

A normal fruiting plant of Lentinus lepedius found growing on the roof 

planks at the valley of the saw-tooth of a cotton weave shed from which 

the sheathing had been removed. 



25 



of the saw-teeth or near humidifiers. These fruiting plants 
generally appear about the first of July, and they grow very 
rapidly, like mushrooms, four days being sufficient for them to 
attain a diameter of two to four inches. 





Fig. 27. 

Abnormal fruiting plants of Lentimis lepedius, two feet long, grown between 

the roof planks and the sheathing of a cotton weave shed. The abnormal 

form is probably due to excessive moisture and darkness. 



The Fames officinalis shown in Figure 28 appears to be more 
exacting in its requirements than the others and while not as 
common it is nevertheless a roof destroyer of considerable im- 
portance. It is more often found on the beams than on the roof 
plank, although the plank is not immune from it. 








Fig. 28. 

Fomes officinalis plants growing on the side of a beam under a roof from 

which the sheathing has been removed for some time. It appeared most 

frequently on the damper and cooler parts of the roof. 



26 




Fig. 29. 

Southern pine roof of a weave shed destroyed in nine years bj- Tramefes 

serialis. 



Fomes roseiis fruiting plants have been rarely found on roof 
planks, doubtless due to the low temperature requirements of 
this fungus. It is frequently found on pulp wood and lumber 
piles. 




Fig. 30. 

Fomes roseus fruiting plants on the end of spruce roof plank that extended 

beyond the brick wall forming the jet of a wea\-ing miU. It was protected 

from the heat of the sun by the shadow of another bxiilding and in summer 

bv the shade of a large tree. 



27 



THE RAPID PROGRESS OF DRY ROT. 

In most cases, the rotting found has taken place rapidly, 
instead of having been, as sometimes supposed, a slow 
continuous process similar to the rusting of iron or weathering 
of stone, and to be looked for chiefly in old buildings. Some- 
times, after the timber has been partly destroyed, the fungus 
growth is arrested, leaving sufficient strength to carry the load, 
and, when the rotted timber is discovered years later, it is as- 
sumed that the destruction has been progressing slowly since the 
erection of the building. 

In a case recently examined, the timbers in an old building 
were found considerably rotted at the bearing ends. Investi- 
gation indicated that the rotting occurred and stopped at least 
twenty-five years ago. In another case, the beams in a weaving- 
mill basement were found seriously rotted at the end of ten 
years. They were replaced with similar beams of the same 
material, with the expectation that they would last another ten 
years at least. Many of these rotted in two years. The living 
fungus growing on the floor against which they were placed 
rapidly invaded the new material, which was green and there- 
fore contained sufficient water to make it subject to immediate 
attack. 

The entire frame of a factory in Canada was replaced after 
three years' service. Nineteen floor beams were removed from 
a Connecticut mill after two years' service, one beam actually 
breaking under a light load. The planking of several weaving- 
mill and paper-mill roofs has rotted so badly that they were 
replaced in from nine to fourteen years. 



28 



EFFECT OF HUMIDITY ON THE PROGRESS OF ROT. 

Dry rot progresses much faster in summer than in winter in 
an ordinary building which is heated and thus has its air made 
relatively dry during the winter months. Moist air gives the 
condition most favorable for rapid rotting. 

The average relative humidity of a building heated to 

60° F. in winter, without artificial moisture, under conditions of 
the external atmosphere which have prevailed in Boston for the 
past ten 3'ears, is shown by the following curve. The curve for 
the summer months is the humidity of the outside air taken 
from the government records. 



> 80 

I- 



g 60 

> 



zo 



RE 


LA 


TIV 


L ) 


lUM 


IDIl 


Y 


OU" 


r 


F j 


>00 


RS 






.-1 


— < 


^ 


^ 










'^ 


"-J 


^ 


^ 




' ' 




> 


)..« 


• »■' 


p- 












♦. 


• 






'"^ 














• 


.• 


!^^ 


5^ 
















> 


\ 


















,,< 


<^ 


^^ 






















\ 


\ 














s< 




^ ' 


























'K 




^•, 




#• 


v< 


A 


































'••( 




••^ 


■V 


'^ 








































<^ 











































JAN. 



FEB. MAR APR. MAY JUNE JULY AUG SEPT OCT 



NOV 



DEC 



Fig. 31. 

Giving the average relative humidity at Boston for the past ten years, both 

out of doors and inside a building heated to 60° F. in winter. 



If the building is colder than the outside air in summer, or 
heated to less than 60° F. in winter, the relative humidity will 
be proportionately higher. 

If there is a source of moisture in the building, such as a moist 
basement, a leaky steam or water pipe, water from drying cloth? 
paper, or moist cotton, or from artificial humidifiers, the air will 
be further moistened. These sources of moisture generally act 
locally, causing a higher relative humidity in one part of the 
room than another. Near a cold pipe, or a cold roof or wall; 
the relative humidity may be increased without change in the 
absolute humidity, that is, the number of grains of moisture in 
a cubic foot of air. The relative, as well as the absolute humidity, 
may be locally increased; for example, by a leak in a steam pipe, 
the presence of a humidifying head, or vapor pot, or a bale of 
moist cotton. In studying the effect of moisture on dry rot. 



29 

one must carefully distinguish between relative humidity 
and absolute humidity. 

Relative humidity is simply the ratio of complete saturation, 
or the per cent, of saturation, of the air at the given tempera- 
ture, while absolute humidity is the actual quantity of water in 
the air, regardless of temperature. The relative humidity corre- 
sponding to a given constant quantity of water in a cubic foot of 
air changes greatly with the temperature; in other words, warm 
air will contain a much larger quantity of water than cold air. 

The amount of water required for saturation, that is, for a 
relative humidity of ioo% at a barometric pressure of 30 inches, 
varies with the temperature, as follows: 

100% Relative Humidity at Grains Water per cu. ft. 

go° F. approximately 15 

80° " " II 

70° " " 8 

60° " ' " 6 

50 4 

40 3 

One gallon of water would produce saturation when distributed 
through 7740 cubic feet of air, at a temperature of 65° F., equiva- 
lent to a room 10 ft. high x 20 ft. wide x 39 ft. long; and a quart of 
water, in the same volume of air, would give a relative humidity 
of 25%. 

The relative humidity at any temperature is the per- 
centage v^^hich the humidity found bears to that required 
for saturation. For example, if air at 70° F. was found to 
contain four grains per cubic foot, the relative humidity would 
be 50%, since eight grains are required for saturation at this 
temperature. Looked at in another way, if external air in 
December, having an absolute humidity of two grains of water 
per cubic foot at a temperature of 30° F., is taken into a room 
heated to 60°, its relative humidity becomes decreased from 
100% to 30%, although its absolute humidity remains almost 
unchanged. 

The most convenient and accurate method of measuring rela- 
tive humidity is by means of a sling hygrometer, which con- 
sists of two thermometers held in a suitable frame, so arranged 
that it can be whirled about rapidly through the air. One 



30 

thermometer has the bulb enclosed in cloth which is moistened 
with water. The evaporation of water from this bulb causes a 
decrease in the temperature which is proportional to the relative 
humidity. This quantity can therefore be found by use of tables 
which accompany the instrument. 

Another instrument in common use in cotton mills makes use 
of the same principle, but the thermometers are fastened to a 
fixed standard, and moisture is continuously supplied to the 
cloth about the wet bulb by means of a wick from a small bottle 
of water. This instrument will indicate too high humid- 
ity unless the air is circulated about the wet bulb by fan- 
ning or otherwise. In a measurement recently made with this 
form of instrument, it indicated 70% as it stood; after vigorous 
fanning, it indicated 55%. 

Neither form of instrument is suited for use in very small 
spaces, such as the opening about the bearing end of a beam, as 
the moisture evaporated will in itself change the relative humidity 
and the circulation necessary for accurate measurement will in- 
troduce further disturbance. The instrument best suited for 
confined situations makes use of the extension and contraction 
of a hair with the relative humidity. A fair degree of accuracy 
can be obtained with this instrument if it is calibrated from 
time to time. 

A case investigated in a cordage factory, where several strips 
about four feet wide rotted in the three-inch plank flooring the en- 
tire length of the factory under spinning machines, which were 
evaporating considerable quantities of water, shows the efifect of 
locally increased atmospheric humidity. The same form of floor 
when not in the immediate vicinity of this humidifying process 
has remained perfectly sound. The average relative humidity 
in the room is from 50% to 60%, while that directly under the 
machines is the greater part of the time at nearly 100%. 

Undoubtedly the growth of all fungi can be arrested by 
moderate drying. Those which grow in basements suc- 
cumb to it quickly, particularly if it is accompanied by 
heating. They all seem to grow most luxuriantly when the 
relative humidity is nearly or quite 100%. In a basement re- 
cently examined, which was 175 ft. wide with windows on one 
side only, the relative humidity varied from about 50% near 
the windows to 100% on the further side, where there was no 



;i 



circulation of air. In the area which was most of the time at 
about ioo%, there was an abundance of fruiting plants of the 
Trametes serialis and Fomes roseiis. The floor had only been in five 
years. The spruce planks were completely destroyed and the 
yellow pine beams somewhat attacked by the fungus. See 
Figure 27. 

Openings were made in the outside walls and a slight circula- 
tion of air obtained, so that the ordinary atmospheric humidity 
was reduced to about 80% to 90%, with the result that the 
growth of the fungus was arrested. 




Fig. 32. 

12" X 16" yellow pine beam and 4" spruce for plank destroyed in five years 

by fungus in a moist basement in a woolen mill in Massachusetts. Scale 

about one-sixteenth natural size. 



In another basement, where these two varieties were growing 
luxuriantly, the Fomes roseus was found only in the parts which 
were at practically 100% humidity most of the time. The Trametes 
serialis was found in the drier parts with an atmospheric humidity 
in the neighborhood of 90% to 95%. 

When ventilation is made use of to stop the growth of fungus 
in a basement, care must be used to avoid locally reducing the 
temperature by introducing cold ventilating air, which will in- 
crease the relative humidity near where the air enters, causing 
precipitation of moisture out of the atmosphere, or "sweating," 
which will increase the rotting at this point. 



32 



DRY ROT AND DAMP ROT. 

There is a close relation between rot and moisture. Tempera- 
ture is also an important factor. The expression "dry rot" is 
used in a vague and meaningless manner. No fungus can grow 
under conditions of dryness or anything approaching it. Some 
of the fungi require more moisture than others, but the most 
important factor which has given rise to the supposition that 
fungus can grow under conditions of dryness, is a property 
possessed to a greater or less extent by many of the fungi, of 
being able to decompose cellulose and liberate water, as is proved 
by the remaining rotten wood showing on analysis an increased 
percentage of carbon. 

The rot always starts locally, in a season crack or near a cold 
outer roof covering which keeps the moisture in this position up 
to or above the fiber-saturation point of the wood. As the fungus 
progresses it forms water from the decomposition of the wood, 
and if the section of the wood is so great or it is so enclosed as to 
prevent the evaporation of this water as rapidly as it is formed, 
the rot will continue at an accelerated velocity and the water 
of decomposition will accumulate in the surrounding wood. 
This condition will be favored if the surrounding atmosphere is 
nearly saturated with water, as such an atmosphere could not 
absorb much more water, or if it is so confined that it cannot cir- 
culate, which will keep it saturated locally near the rotting 
wood. Therefore the rate of evaporation from the wood will be 
retarded. This is always assuming that the wood at the start 
is comparatively dry. If the wood at the start is saturated or 
filled with water, in other words, water-logged, fungus cannot 
grow in it. Such wood would be prevented from rotting by 
being kept in a water-saturated atmosphere which would pre- 
vent it from losing water. 

Some fungi require more moisture than others for rapid growth. 
Some are rarely found, except in moist basements, while others 
are most frequently found on roof planks. This is generally 
attributed to this moisture requirement, which is doubtless a 
factor, but another important factor is probably the temperature. 



33 



LOCAL DIFFERENCES IN EXPOSURE TO MOISTURE. 

The relative humidity of air in a room, or basement, 
sometimes is very different in places only a few feet apart, 

and, in studying cases of infection, careful note should be taken 
of these differences. 

An ordinary method of measuring the atmospheric humidity 
by means of a sling hygrometer gives the average humidity 
over a considerable space. An example is shown in Figure ^^ 
of locally increased relative humidity. 




Fig. 33. 

Floor beams rotted off by increased relative atmospheric humidity caused 

by a cold-water pipe.^ 



In this case, a cold-water pipe passes under several beams in 
a basement, the average humidity of which is in the neighbor- 
hood of 90%. The lower temperature in the vicinity of this 
pipe causes an increased saturation up to 100% at the pipe. 



1 The distinction between relative humidity and absolute humidity should be 
clearly understood. When the term humid or humidity is used in every-day talk, 
relative humidity is meant, not absolute. Relative humidity is the percentage of 
complete saturation that the air happens to contain at the given time and changes 
with the temperature, while the absolute quantity of water per cubic foot of air 
remains unchanged. The presence of the cold-water pipe shown above increases 
the relative humidity of the air near it simply by lowering its temperature, while the 
number of grains of water in each cubic foot of this air remains almost unchanged. 



34 

* 

The beams directly over it are rotted for a distance of eighteen 
inches to two feet away from the pipe, as can be seen in the 
photograph. 

Dry and wet are only relative terms. The degree of dry- 
ness is of the greatest importance. The slight difference of a few 
per cent in the relative humidity is sufficient to stop the growth 
of certain fungi. The growth of the fungus depends more upon 
the relative humidity than upon the number of grains of water 
per cubic foot. It is also doubtless considerably influenced by 
the temperature, as previously stated. The effect of saturation 
of moisture is not limited to the air. but extends to the interior 
of the timber, as is shown by the rotted tank stave shown in 
Figure 34. 

Weaving-room and paper-mill roofs are frequently found 
with a sound shell both inside and out. and the interior entirely 
rotted away. Sometimes the zone of greatest rotting is nearer 
the outer roof covering, and sometimes nearer the inside of the 
building, according to the relative atmospheric humidity. See 
Figures 43 and 44. 

Certain processes of manufacture require the atmos- 
pheric humidity to be regulated within narrow limits.^ 

If it so happens that this humidity is sufficient to keep the 
timber or planking near the condition required for the most rapid 
growth of a common timber-destroying fungus, as is frequently 
the case in weaving and paper mills, exceptional care must be 
given to selecting a resistant variety of timber, and to giving it 
a suitable antiseptic treatment in order to prevent serious rot- 
ting. If. however, conditions of manufacture do not demand 
high humidity, and it can be kept down to S'^''.c during most of 
the time, there is little danger of serious rotting of good timber 
if it is dry and sound when installed. 

It is probable that a very important factor in the resist- 
ance of several woods to fungus is the presence of some 
moisture-resisting material such as resin, which prevents 
sufficient water from being absorbed at the ordinary range of 

1 Cotton carding rooms are frequently maintained at a relative humidity of 
50*^ to 60^, and weave rooms from 60*^ to So'^. Paper mills are much of the 
time at nearly 100 "^c at the ceiling over the paper machine. In many textile proc- 
esses, the humidity is maintained at a high percentage contiuuouslj- daj- and night 
the year round, the tendency being constantlj' towards higher humidities. 



35 

atmospheric saturation for the requirements of common fungi. 
On the other hand, the presence of hygroscopic materials in 
wood, which cause it to absorb larger amounts of water, in order 
to come into equilibrium with a given atmospheric saturation, 
would render it more susceptible to attack by fungi. 

Most of the cases of the rapid destruction of the frames of 
new buildings have been caused by the use of timber already 
completely permeated with living fungi when it was put into the 
structure. 



36 



EXTREMES OF WETNESS AND DRYNESS BOTH 
PREVENT ROT. 

Figure 34 shows a plank from the bottom of a tank, in which 
the fungus grew through a narrow space in the middle, the in- 
side next the water being too wet for it and the outside next the 
air, too dry. 

That wood-destroying fungi cannot grow under water, or with 
the wood cells filled with water, is proved by many examples. 

One of the fine points in the successful design of wood-stave 
pipe from two feet to ten feet in diameter, for conveying water 
under pressure, is to design its staves so thin that the pressure 
will keep the wood saturated; then it will last for long periods 
without decay. 

Penstocks have sometimes been covered with clay to prevent 
evaporation and keep the cells fidl of water. 




,^r-*^ 



Fig. 34- 
23^" plank from a water tank. 



Wood of great antiquity has been found buried in clay, 
in a perfect state of preservation.^ Piles under an old 
London bridge were found sound after being in the water 600 
years.^ The roof beams of the Basilica at Rome were found 
sound after a thousand years' use under conditions of dryness.^ 
In deep test borings for engineering structures, samples of buried 
logs are brought up in a good state of preservation after burial 
in wet earth since the glacial epoch. 

1 " North American Gymnosperms," Penhallow. 

2 "Destruction of Wood by Fungi," Buller, Science Progress, Vol. Ill, No. 2. 

3 "A Treatise on the Resistance of Materials," D. V. Wood, 1883. 



37 

In popular phrase, "rot comes between wind and water," or 
in scientific terms at a point at which the wood substance of the 
cell walls is saturated with water and the cells contain mostly 
air, or with spruce wood when it contains from 30% to 40% of 
water. 

The weaving rooms of cotton mills are frequently main- 
tained at a saturation of moisture of 70% to 80% during 

working hours. With 70% saturation and a temperature of 
80° F., a decrease in temperature of 12° at night would cause 
precipitation, or increase the saturation to 100%. Rot in roof 
planks and the bearing ends of beams is doubtless chiefly due 
to this condition. The roof and walls of a manufacturing build- 
ing are colder than the air in the room for a considerable part of 
the year, therefore the air in contact with these cooler parts of 
the structure will be at a higher relative humidity than the 
average of the room. In the summer months, when these con- 
ditions do not hold, the outside humidity is high much of the 
time, so that the roof planks and beam ends in a highly humidified 
mill get little chance to thoroughly dry out at any part of the year , 
and antiseptic treatment of the timber is the only certain re- 
liance against decay. 

The Limits of Dampness Required for Growth of Dry-Rot 
Fungus. 

Dry-rot, or Merulius lachrymans, fungus, will grow on the sur- 
face of wood at atmospheric saturations from 96% to 100%. ^ 
It will grow inside of large beams of susceptible material at a 
much lower atmospheric saturation. In one case investigated, 
the room was maintained at less than 70% relative humidity, 
yet a large proportion of the beams supporting the second floor 
were destroyed within two years after the factory was completed. 
This fungus was doubtless brought in in the timber. 

A possible source of moisture for supplying the require- 
ments of a fungus growing inside a large beam is the 
decomposition of the wood itself. Chemical analysis shows 
rotted wood to contain less hydrogen and more carbon than the 
original sound wood,- therefore the hydrogen part of the cellu- 
lose, or lignine molecule, is more strongly attacked than the 
carbon part. This would result in the formation of water if the 

1 " Hausschwammforschungen," Vol. VI, p. 308, Moeller, Jena, 191 2. 

2 " Cellulose," Cross and Bevan, 1903, p. 239. 



38 

decomposition is accompanied by complete oxidation. Wood 
undergoing bacterial decomposition under water forms marsh 
gas in large quantities. This may be formed to some extent 
when wood rots in the air, but apparently considerable water is 
also formed, as shown by some direct measurements by Dr. 
Mez.^ This explains why fungus may thrive for some time in an 
atmosphere of lower relative humidity, if established deeply in 
beams of large size, from the interior of which the water formed 
by the decomposition of the wood is but slowly evaporated. 

In a recent case, fungus appeared on the floor beams under a 
weave shed, about 300 feet wide, within a 3'ear after the building 
was completed. The beams were about four feet above a damp 
swampy soil. The builders, appreciating that the conditions 
were unfavorable, gave the beams a brush treatment with a coal- 
tar preservative, and provided large open windows, at frequent 
intervals, for ventilation. The beams evidently contained liv- 
ing fungus when received. The ventilation prevented growth of 
the fungus on the surface of the wood for fifty or sixty feet from 
the windows. Beyond this, an abundant growth appeared. 
Measurements showed the relative humidity to be nearly 100% 
in the middle of the building, and 60% at forty feet from the 
windows. 

Ventilation Not Always a Cure. 

Ventilation is generally the first preventative measure sug- 
gested. Dry wood, which is placed in an atmosphere well below 
the moisture requirements of fungus, is undoubtedly incapable 
of infection; but, ventilation does not necessarily cause drying, 
as the wood will come into equilibrium with the moisture in the 
air and will become drier or wetter in proportion to the relative 
humidity of the air with which it is ventilated. Therefore 
timber ventilated with moist air may have its rate of 
rotting accelerated rather than retarded. As an example, a 
thoroughly waterproof covering for a column, which had been 
completely dried, would be more useful than a hole through the 
center for ventilation, if this column was used in a moist paper 
mill. 

Paint Sometimes Retards, Sometimes Accelerates Rotting. 

A heavy coat of paint may accelerate or retard the rate of 
rotting, depending upon whether it prevents the wood from ab- 

' " Der Hausschwamm," Dr. Carl Mez, Dresden, 1908, p. 192. 



39 

sorbing or giving up moisture. The condition most commonly 
met, in which paint causes rotting, is when it is applied to green 
timbers containing much water. With dry, sound timbers, 
which are to be placed in a moist atmosphere, a paint will doubt- 
less prove beneficial in proportion to its waterproofing power. 
''Cold-water " or "fireproofing " paints, containing hygroscopic 
materials, would be expected to accelerate the progress of rot, 
because they would attract moisture from the air and increase 
the moisture in the wood, as in the case of a building in Italy, 
in which chloride of lime was used as an antiseptic, with the 
result that the chloride of calcium attracted moisture and caused 
the rapid destruction of the building by fungus. 

The conditions required for germination and growth of 
the Merulius lachrymans often have been mysterious. 

The spores germinate in an eccentric manner and frequently 
refuse to grow to fruition on their customary host in artificial 
cultures. Hartig stated that an alkaline medium is necessary, 
but it has since been shown by several investigators that an acid 
medium is required for the growth of the plant. The degree of 
acidity and the kind of acid is important. Falck shows that 
acetic, formic or carbonic acids are poisonous to it, while malic, 
citric and tartaric, in dilute solution, favor its growth. 

Long Life of Dormant Fungi. 

Dry-rot fungi have two methods of reproduction and 
can remain a long time in a resting state. The common 
reproductive body, corresponding to the seed of higher plants, 
is called a spore, and grows over the surface of the plant. They 
are of brown color and therefore may be easily distinguished 
from the surrounding sterile growth, as can be readily seen from 
Figures 14 and 15. The spores are microscopic in size, being 
about .0004 of an inch long and .0002 of an inch broad. A single 
plant produces many millions and their small size allows them 
to float long distances in the air. 

Under unfavorable conditions for growth, such as insufficient 
moisture, some of these destructive fungi assume a form of re- 
production different from that by which they ordinarily spread. 
In this form, the growing plant separates into small sections 
which can sprout and grow again when favorable conditions arise. 
It can remain in this resting state for a considerable time in 



40 

air-dry wood. Some of this dormant fungus is shown in the 
photo-micrograph, Figure 20. 

I have some specimens from a beam which was removed from 
a mill two years ago. Cultures from time to time show the 
Merulius lachrymans, which it contains, to be still living. ^lez ^ 
mentions a case in which this variety of fungus remained alive 
for four years and eight months in a dry museum cabinet. 



1 " Der Hausschwamm,'" ' Dr. Carl Mez, 1908, p. 63. 



41 



HOW THE DRY-ROT DISEASE IS SPREAD. 

This disease is chiefly spread by direct contact, but living 
spores carried in the air can take root when they find a favor- 
able resting place. 

Fungi are frequently carried in lumber ^ and spread by plac- 
ing it in large piles with scant ventilation. As a result of this, 
beams are often found more deeply infected in the middle than 
at the ends. 

The separation of lumber in the piles by the use of sticks 
containing living fungus is another fruitful source of infection. 
Susceptible timber placed on rotten supports near the earth 
quickly becomes diseased. This is now avoided in several lum- 
ber yards by the use of concrete supports as shown in Figure 35. 




Fig. 35. 
Concrete supports for lumber piles. 



1 Bulletin No. 13, U. S. Division of Forestry, p. 118. 



42 



HEAT AND DRYING ARE USEFUL IN STOPPING 

ROT. 

Often an infected building can be sterilized by skillful 

use of its own heating system. Merulius lachrymans is 
particularly sensitive to heat, a temperature of io8° F. for 
three hours, or 115° for one hour, being sufhcient to kill it. ^ 
It is also killed by complete dryness.^ But ordinary air drying 
does not destroy it. 

The particular varieties of fungi that destroy roof planks 
are undoubtedly more sensitive to dryness and less sensitive to 
heat than dry rot. It is therefore probable that heating a weave- 
shed or paper-mill roof will have little beneficial effect unless it 
is infected with lachrymans or Coniophora, which is improbable 
except in a new building. 

Heat as a means of destroying lachrymans and con- 
iophora in mill beams was tried, at the suggestion of the 
writer, on a large mill, in Canada, which was badly infected 
throughout; but later it was found that the disease had already 
progressed so far before the heating was applied that the struc- 
ture had become unsafe, therefore the beams had to be replaced. 
This removal of a thousand beams and columns gave an excel- 
lent opportunity to test the efficiency of the previous heat treat- 
ment by cultivating samples from those beams in which the 
infection was the deepest. This treatment had comprised 
heating the mill four times, to about 115° F., by use of the steam- 
heating system in warm weather, from Saturday noon until 
Monday morning, the temperature being carefully regulated 
by use of thermometers placed at the ceiling. 

In applying this heat treatment in mills protected against fire 
by automatic sprinklers, care must be used not to open or per- 
manently injure the sprinkler heads. The temperature of the 
air should be kept 50° below the melting point of their fusible 
solder, which ordinarily is about 165°. 

Specimens were cultivated from forty of the badly rotted 
beams and only four showed living fungus. One hundred and 
three beams removed and left on the ground for several months 
were examined superficially, and, in all of these, only six showed 

1 " Hausschwammforschungen," Vol. I. 

2 " Hausschwammforschungen," Vol. VI. 



43 



suspicious threadlike growths. The window frames and hollow 
roof were not sterilized by this treatment. Some of the few 
living cultures found came from the ends of beams which were 
imbedded in the brickwork where the heat could not readily 
penetrate, and some of the beams left on the ground may have 
become reinfected. 

On the other hand, beams removed from the mill before it 
was heat-treated showed a vigorous growth of fungus on cul- 
tivation, and also the formation of normal fruiting plants when 
left lying in the yard. 

While the results of this one practical experiment are not 
absolutely conclusive, they are very encouraging and indicate 
that the small cost of putting steam on the heating coils 
is well worth trying, if there is any suspicion of dry rot in 
a new building. 

Heating will probably prove more efficient in the few scattered 
superficial infections of a mill just completed than it did in this 




Fig. 36. 
Threadlike sterile fungus plant on end of a rotted mill beam. 

quarter natural size. 



Scale one- 



44 



mill where the growth had been in active progress for two years 
or more and had deeply penetrated the susceptible material. 

The special heating will also increase the rapidity of drying 
and thereby tend to limit the spread of the disease through the 
agency of the rapidly growing threadlike plants. These growths 
pass rapidly along the splines of moist floor planks and through 
holes in moist columns, or openings between double beams, and 
can thereby quickly reach most of the susceptible material in 
the building. The most serious cases of rapid spread of the 
dry-rot fungus that I have yet investigated have occurred where 
sappy or nonresistant material, exposed to the weather, remained 
in a water-soaked condition until it was covered, so that it 
could not dry out. The drying will also arrest other varieties 
of fungi than the lachrymans. 



45 



HOLES IN COLUMNS AND DOUBLE BEAMS WILL NOT 

PREVENT ROT. 

One of the reasons given for bored columns and double 
beams has been to prevent dry rot, and considerable im- 
portance has sometimes been given to this feature.^ 

Undoubtedly columns with holes through them, and thinner 
beams, would dry out quicker if given a chance to season, but 
the common custom of boring green or wet columns just before 
they are put in place in the building, and using moist lumber 
for double beams, leaves ideal places for the growth of fungus, 
as the air in the openings will be kept saturated with moisture 
if no means of circulating it is provided, as is generally the case. 
The holes in the columns have the additional objection of forming 
a convenient passageway for the fungus to pass rapidly from 
floor to floor before the building has dried out. 

Untreated Carolina pine used for interflooring sometimes 
serves not only to infect the mill, but to carry the infection to 
all susceptible beams or planking in the floor. 




Fig. 37. 
Central cross section of 10" x 10" Southern pine column bored from opposite 
Holes do not come together in center and fungus can be seen in 
each hole. 
Engineering News, Vol. LXII, igog, p. 620. 



ends. 



46 




Fig. 3S. 

10' s 10' column, shown in cross section in Fig. ss- split through the holes, 
showing the fungus inside them more clearly. The holes are one and one- 
half inches in diameter. 




Fig. 39. 

Cross section^ center of a 10' s 10' loblolly pine column, badly rotted, 

in a cotton factory- after three years' ser\-ice. Note that the hole through 

this column did not prevent it from rotting. 



47 



SLOW-BURNING CONSTRUCTION. 

The following drawings show two examples of slow-burning 
factory construction which are in common use. One, a several 
story building of moderate width; the other, a one story building 
which may have any width, as it is lighted by means of windows 
in the saw-tooth roof. The basement of the latter form of con- 
struction gives some trouble from rotting if the building is 
located on moist ground, owing to the fact that it is difficult 
to get a circulation of air through this basement in the widths 
of 200 feet or more, commonly used in weaving mills. The belts 
and belt holes provide some air circulation, but if the air in the 
room above is highly humidified and the basement is cool this 
may increase rather than decrease the moisture. 




Fig. 40. 

Standard form of slow-burning mill construction, with beams spaced from 
8' to 12' on centers, and heavy plank floors. 



48 




'■''''"Ttiiaf^ 



Fig. 41. 
Standard slow-burning factorj* building with, saw-tooth roof such as is fre- 
quently used for weaving mills. 



Laminated Floor. 

In slow-burning timber construction it has been customary, 
in many cases where an unusually stiff floor is required, to use 
2" X 4" or 3" X 6" planks, spiked together on edge, for forming 
the floors. This so-called laminated construction is very 
treacherous so far as rotting is concerned, particularly if 
the planks are not thoroughly dry when the building is 
covered in. In buildings several stories high, it is customary 
to lay the plank of the lower floors before the walls of the upper 
stories are complete, thus leaving them exposed to the weather 
until the roof is put on. Sometimes the floors become thor- 
oughh^ water-soaked by means of the numerous cracks between 
the planks. The evaporation of this water is retarded by the 
great thickness of the floor thus formed of plank on edge and 
by the top flooring. This moisture encourages rotting. In 
storehouses, for which this form of floor is frequently used, 
the conditions are worse than in the manufacturing rooms, 
because the storehouses are seldom artificially warmed in winter, 
thereby giving less opportunity for drying. Several such cases 



49 



have been reported. The following figure shows two pieces, 
3" X 6" X 24", cut from some Southern pine planks from such a 
floor in a Chicago storehouse, after six years of service. These 
floors were water-soaked by rains before the roof was put on, 
and, as the building was not heated, the process of drying was 
very slow, with the result that the floors throughout the entire 
building were considerably rotted. 




Fig. 42. 

Pieces cut from 3" x 6" Southern pine planks removed from the laminated 

floor of a Chicago storehouse after six years' service. 



50 



ROOF DESIGN. 

The roofs of highly humidified weave sheds, paper mills and 
bleacheries filled with steam are prone to rot and therefore 
special consideration should be given their design with a view 
to reducing this trouble. In addition to the expensive up-keep 
resulting from the rot, damage to goods and machinery caused 
by water dripping from cold roofs is frequently the more trouble- 
some and expensive feature. 

Both the rotting and the sweating arise from the same cause 
and can be reduced by the same remedy. This remedy is to 
avoid the reduction of temperature to the dew-point at the 
roof. So far as roof design is concerned this can be brought 
about by increasing the heat and heat insulation of the roof, 
thereby reducing the escape of heat through thin and poorly 
insulated roof planks, ventilators, skylights, roof drains, etc. 
and by placing heating pipes in such position as to supply the 
heat unavoidably lost. Care should be taken to prevent the 
penetration of moisture into, and its precipitation within or 
above, the roof planks. This is a common occurrence. The 
fungus plant which causes the rot thrives in the interior of the 
plank, where sufficient moisture has penetrated to make its 
growth possible, as shown in Figure 43. It might be thought 
at first sight that the splines in this plank started the rot, but 
Figure 44 shows planks which were put together with dowell pins. 
It will be noted that the sound wood stops at a very definite 
line in each case. 

All of the wood-destroying fungi require atmospheric con- 
ditions very near if not quite at the dew-point or fiber saturation 
of the wood for their best growth. This limiting condition is 
inside the roof plank, as shown in Figure 43, and upon this depends 
several important details in the design of roofs. 

It is always to be noted in removing a rotted roof that the 
destruction is more complete over the beams than elsewhere. 
At these points the rot has frequently not only destroyed the 
entire plank, as shown in Figure 45, but has extended some dis- 
tance into the beam. 



51 




Fig. 43. 

Four-inch longleaf pine roof planks, rotted through the center, from a paper 

mill in Maine. 



52 




Fig. 44. 

Four-inch spruce plank from bleachen* roof. Upper half rotted away while 

the lower portion is still sound, owing to moisttire being sviitable for fiingus 

at the top and insufficient at the bottom. As the wood rots, the insulation 

becomes less and the moisture and rot graduallv extend downward. 




Fig. 45. 

Ends of roof planks rotted over the supporting beam. The rot has also 
extended three or four inches into the beam. 



53 



This is caused by the above-mentioned moisture limit or 
point at which the water absorbed by the wood is favorable to 
fungus growth. This can probably be more clearly shown by 
an example of conditions commonly found in weaving mills. 
The room temperature approximates 70°, the outside tempera- 
ture perhaps averages in winter weather 30°, and the dew-point 
of the air in the room is around 60°. Assuming a uniform heat 
conductivity for the roof material it would be expected that 
the dew-point, that is 60°, would be found within and near the 
center of the roof plank, however thick it is. As rotting takes 
place just above the fiber saturation of the wood, it would be 
expected that it would begin above the dew-point limit where 
moisture is precipitated, and be limited by this line which will 
be somewhat irregular and dependent upon the thickness and in- 
sulating power of the roof. Therefore, when a thick supporting 
beam is encountered, the rot line will be brought down below the 
lower surface of the plank and into the beam itself, entirely 
rotting off the planks at their bearing ends, as shown in Figure 45. 
Wood, like cotton and. other hydroscopic substance, absorbs 
more or less moisture from the surrounding atmosphere depend- 
ent upon the relative humidity. 




Fig. 46. 

Section of roof plank and supporting beam showing the line of moisture 
limit at which fungus growth will stop. 



That the actual limit is followed with definiteness is demon- 
strated in Figures 43 and 44, showing sections of roof planks 
removed from two factories. 

The obvious remedy is to make the bearing no wider than the 
thickness of the plank. This can be accomplished when wide 



54 



beams are required by champhering off their upper corners, as 
shown in Figure 47. 




Fig. 47. 

Section through roof plank and beam showing a method of reducing rotting 

over beams. 



This should increase the life of the roof plank and protect 
the beams, while the not infrequent custom of placing ornamental 
moldings at the upper edge of the beam accelerates the destruc- 
tion by bringing the rot line entirely outside the bearing end of 
the plank, completely destroying the supports before the re- 
mainder of the plank is deeply affected, as shown in Figure 48. 




Fig. 48. 

Section through roof plank and beam showing effect of molding in bring- 
ing moisture line limiting fungus growth outside the supports, thereby rot- 
ting off the ends of the planks. 



Sheathing acts in a similar manner by keeping the heat of 
the room away from the plank and bringing the rot line down 
below its lower surface, thereby causing the rapid destruction 
of the entire roof plank, as shown in Figure 40. 



55 




Fig. 49. 

Roof planks of a New Bedford weave shed from which the sheathing has 
been removed. The planks were destroyed in nine years. 



It would be logically concluded from this, that the place for 
the insulation is on the outside of the roof instead of the inside, 
and that anything which would prevent the penetration of 
aqueous vapor into the roof plank or remove this vapor from 
the interior of the roof more rapidly than it could penetrate, 
would be expected to increase the life of the roof; therefore, a 
double roof suggests itself with the outer part of rot-resisting 
material, and the inner part having sufficient strength to support 
the load as well as having the necessary qualities for the finished 
mill ceiling. 

Between the two roof planks there should be a layer imper- 
vious to aqueous vapor to prevent moisture from penetrating 
the outer plank and reducing its heat-insulating power. The 
outer part could consist of partially rotted planks removed 
from a previous roof of low-grade new lumber. The more sap- 
wood it contains the better, as this absorbs creosote better than 
heartwood. Whatever kind of wood the outer part of the roof 
is, it should be completely penetrated with hot creosote or other 
efficient antiseptic so as to sterilize it and prevent the later 
development of fungus. Such an outer insulating covering will be 
found as practicable for a concrete roof as for a wood roof. The 
poor heat-insulating power of concrete makes it necessary to thor- 
oughly insulate it to prevent sweating with moist occupancies. 



56 



Tar and grekvel rooffn^ or eqvivalenh 
Thoroughly creosolecl low ^rade plank 




/s Air Space Three thicknesses of tarred paper 
1/2" "Hiin plank of good c^ualil-y siiil'flble for 
carrying 3 thicknesses of tarred paper and 
forming the finished ceiling. 

Fig. 50. 



In some cases rotting has been discovered in its early stages 
in saw-tooth weave-shed roofs sheathed underneath. Experi- 
ments are now under way with a view to removing the moisture 
from the space between the sheathing and roof plank of such 
a roof by making small holes from this space to the outer air, 
as shown in Figure 51. 




Fig. 51. 
Holes to vent the hollow space in a sheathed roof to the outer air. 

The idea is to allow the aqueous vapor in this space to escape 
by the breathing caused by variations in temperature and baro- 
metrical pressure as recommended by Mr. Arthur N. Sheldon for 



57 



double factory windows.^ These experiments have not been 
under way long enough yet to warrant positive conclusions. 
There seems to be no reason why they should not increase the 
life of the roof somewhat. 

It is evident that if the wood-destroying fungi require a cer- 
tain amount of moisture for active growth, they may be as effec- 
tively killed, or at least put into a harmless resting state, by 
depriving them of this moisture as by poisoning with antiseptic 
mixtures. Experiments are in progress with a view to testing 
the practical application of this theory by placing a heat-insula- 
ting roof similar to that previously described over an old roof 
in which rot has already made considerable progress, although 
it still has sufficient strength to carry the load. If this method 
proves effective it will be simply necessary to apply such an 
insulating outer covering to a roof in which rot has been dis- 
covered in its early stages, while there is still sufficient strength 
in the old roof to carry itself and the added load. This insulating 
covering can be applied much more cheaply and conveniently 
than the old roof can be removed and replaced, and the old 
roof will still have its full usefulness. 

The following photographs show such an insulating outer 
covering being applied to a weave shed in which rot has already 




Fig. 52. 

Insulating covering consisting of Y^" creosoted boards and a Y^' air space 
being applied to a saw-tooth weave-shed roof. 

^jTransactions American Society of Mechanical Engineers, Vol. XXXI, 1917. 



58 



started. The %" boards used for heat insulation are of Southern 
pine sapwood and were treated on the ground in an open tank. 
A penetration of from four to twelve pounds per cubic foot was 
obtained. Sections of some of the boards are shown in Figure 88. 
The following photograph, Figure 52, shows the boards being 
applied to the roof. The treating tank is shown in Figure 87. 

When the creosoted boards were put on the roof the slag of 
the old roof was scraped off of one bay with chisels. This involved 
considerable expense and somewhat damaged the tarred paper; 
therefore, on the remainder of the roof the loose slag was simply 
swept off with stiff brooms. The 2 x J^" sleepers were then nailed 
on, leaving a J/g" air space under the insulating boards, the 
old Barret specification roofing remaining below the insulating 
covering to prevent the moisture from coming up into the air 
space from the highly humidified air in the room below. The 
present 23^" spruce plank roof was installed fourteen years ago 
and has commenced to show unmistakable signs of rotting, al- 
though it still has sufficient strength to support itself and the 
new insulating covering. 

The location of the rot and the extent to which it has pro- 
gressed is indicated by black marks of the extractive material 
on the white paint of the beams and planks beneath, as shown 
in the photograph, Figure 10. The plan of the roof, on which 
the dark streaks are plotted as short black lines coming out 
from the lines representing the beams, shows clearly the influ- 
ence on the rotting which the heating pipes around the sides of 
the building and the ventilators on the roofs have exerted. See 
Figure 11. The extra heating pipes on the side walls kept the 
parts of the roof towards the outer walls slightly warmer than 
the remainder, and therefore reduced the moisture below the 
limits of the requirement of the fungus causing the destruc- 
tion, while the heat escaping through the ventilators precipitated 
the moisture locally and accelerated the destruction. 

The indication of rotting given by these black lines of extrac- 
tive matter can prove very useful in giving warning of a dangerous 
condition in the roof planks while there is still time to apply 
an insulating covering and save the roof for some years at least. 
Replacing the rotted planks of such a roof as this is by no 
means an infallible remedy, if the insulation or heating is not 
changed to keep the temperature above the dew-point. Figure 
II shows part of two bays which are only two years old and 



59 




Fig. 53. 

Showing sections of spruce planks containing considerable sapwood which 

have rotted in three years on a weave-shed roof. 



which are now the worst rotted planks in the entire roof, due 
doubtless to the lumber which was used on these two bays con- 
taining considerable sapwood and having been kiln dried; there- 
fore, when subjected to the highly humidified air of the weaving 
mill it swelled and made a tight surface, which kept the liquid 
water in, which had passed into the wood as a vapor and con- 
densed in the cooler interior. The extent to which the sapwood 
of these planks has rotted in three years is shown in Figure 53. 

The fungus plant most active in this destruction appears to 
be the Lenzites trabea, some imperfect specimens of which are 
shown in Figure 23. 



60 



A vacuum and pressure process of treatment would probabh* 
give a more uniform penetration than the open-tank process, 
but it is frequently difficult to get vacuum and pressure treated 
lumber promptly, particularh" in small quantities. 

This form of insulation will considerably increase the life 
of a new roof, or a new roof can be made of heavy plank 
thoroughly creosoted and sheathed underneath \N-ith asbestos 
lumber or equivalent, leaving a thin air space, the sheathing 
serving as a painting surface and to prevent dripping and to 
annul the fire hazard of the creosote. 

An important cause of local rotting in roofs is ventilating 
pipes, roof drains and skylights, or other parts which radiate 
more heat than other parts of the building, thereby keeping 
the near-by lumber cooled to the dew-point. 

An example of this is shown in Figure 54, in which a roof drain 
has radiated sufficient heat to rot the roof for some distance. 




Fig. 54. 
This iron pipe for carrj'ing away rain water from the roof has radiated 
sufficient heat to precipitate water on the near-bj- roof and cause it to rot 



This is much more serious when columns are used for con- 
ducting rain water from the roof, and the main supporting timbers 
surround them at their bearing ends. In this case the water 
precipitated by the cold pipe is absorbed b}- the beam which is 
rapidly rotted, thereb}- weakening an important support of the 
structure. Such a case is shown in Figure 55. Sometimes this 



61 





I i / : 

1 ■ / •■ 'I 

1 / ^ I 

^.- I ^ ^ ! ^ ^ 




Fig. 55. 
Cast-iron column used as a drain pipe for rain water has precipitated water 
on and seriously rotted the beams which enclose it. 



water is conducted through season cracks the entire length of 
the beam, weakening it for 20 or 30 feet as shown in Figure 56. 




Fig. 56. 

Beam rotted for some distance from column serving as rain-water conduc- 
tor which it enclosed. 



62 

Ventilators or skj-lights are particularly pernicious in this 
respect, almost always rapidly- rotting the roof for lo or 15 feet 
from them, as shown in Figure 62. 

The remedy for this defect in design is to proWde sufficient 
heat insulation about the drain pipe or ventilator to make the 
escape of heat here no more than at other parts of the roof. 
Roof drains and closet vent pipes can be covered with insulating 
coverings such as are commonly used on heating pipes. Drain 
pipes should be kept separate from important structural sup- 
porting beams of wood. Ventilators should be protected by 
heay\* wooden covers when not in use in cold weather. Double 
windows should be used, and near skylights and other windows 
where it is impracticable to reduce the radiation, additional 
heating pipes should be pro\"ided to compensate for the excessive 
loss of heat. Such heating pipes should be carefullj' arranged 
to avoid setting up air currents which will continuously deposit 
moisture on the cold ceiling or windows. 



63 



ARRANGEMENT OF HEATING PIPES. 

Modern weaving buildings have very large roof and window 
areas exposed to the cold winter temperature, the result being 
that the part of the roof plank which is at or below the tempera- 
ture of the dew-point of the air in the building absorbs sufficient 
water to come within the requirements of some of the common 
wood-rotting fungi. The location and extent of the heating pipes 
will generally be found to have a direct bearing on the location of 
the parts most rapidly destroyed. 

In one New Bedford weave shed, shown in Figure 57, a heating 




Fig. 57. 

Steam pipes half the length of this bay have prevented rotting, while in 
the other half the roof planks were entirely destroyed. 



64 



coil extended half the length of a bay. The part of this roof 
over the heating coil has been on eighteen years and is still in 
service, while the remainder of it was entirely destroyed and 
replaced. The center saw-tooth in a weave shed 500 x 350 feet 
had the main steam pipe supplying all of the circulation at its 
base and extending three-quarters the length of the building, 
while the circulation pipes were in the customary location under 
the windows. This saw-tooth is apparently in a fair state of 
preservation as far as the steam pipe extended, fungus growths 
commencing directly at the end of this steam pipe, as shown in 
Figure 58, while the remainder of the roof, most of which was in 
the condition shown in Figure 49, has been replaced after nine 
years' service. 

It appears that better results can be obtained by locating 
part of the steam pipes at the back of the saw-tooth farthest 
from the windows, as shown in Figures 60 and 64, and part of 
them at the top of the saw-tooth, to compensate for the heat 
lost through the windows and reduce the air circulation. In at 
least one case where pipes were located three on each side of the 




Fig. 58. 

Main steam pipe under the lower part of this saw-tooth prevented rotting 

as far as it extended; immediately beyond the cross pipe where the main 

pipe ends, fungus plants are seen in roof planking. 



65 



bay, as shown in Figure 60, the roof is still in service at the end 
of seventeen years, although other parts of this same roof with all 
heating pipes under the windows have rotted and have been 
replaced. 




Fig. 59. 

Example of roof planking on a saw-tooth that is comparatively sound, while 
remainder of roof was replaced after nine years. The main steam-heating 
pipe that supplies the building extends along the base of this saw-tooth. 








Fig. 60. 

Roof planking that is in good condition after seventeen years of service, while 
other saw-tooth roofs in same building have decayed. Part of the steam-heat- 
ing pipes in this bay are at the back of the saw-tooth, while in those where 
rotting occurred, they were all in the usual position under the windows. 



66 





Fig. 6i. 

Example of roof planking decayed about the skylights, where the tempera- 
ture was somewhat reduced by radiation through the glass. 








/mm 


Mi 






'/" 








/ 


' # 


^-^ 


•*.-,■■ 







Fig. 62. 

Example of roof planking and beam decayed near a ventilator in a saw- 
tooth, due to radiation of heat through the thin metal cover of the bottom 

of ventilator. 



67 

The success of this arrangement in preventing rot will depend 
not only upon the location of the steam pipes but upon the abso- 
lute amount of heat supplied. This must be sufficient to keep 
the roof temperature above the dew-point. In one case a 3" 
roof of excellent longleaf pine has rotted in seventeen years with 
three steam pipes on each side of the bay. The trouble here 
appears to be that while the pipes were well located sufficient 
heat was not provided to keep the roof temperature above the 
dew-point of the air, which was highly humidified by means of 
vapor pots. 

Details of construction such as thin metal ventilators, metal 
roof drains, skylights and windows, which radiate more heat 
than other parts of the roof and thereby keep the air in their 
vicinity cooler than in other parts of the building, will accel- 
erate the destruction. 

The cure already mentioned is to prevent the escape of heat 
by increasing the heat insulation of the roof by an outer non- 
conducting covering or by making it double. 

It may be found more convenient to provide more heat rather 
than to reduce the loss by increasing the insulation. Some 
insulation should be provided in all cases however, and care 
should be given to preventing the moisture from penetrating 
the roof plank and condensing on the cold outer roof covering. 
This is particularly important if absorbent felts have been used 
on the outside of the roof for insulation, in which case the mois- 
ture will reduce the insulating power and encourage fungus 
growths. 

Moisture carried by air currents set up by the heating pipes 
is an important factor in causing rot in roofs. The arrangement 
of heating pipes commonly found in saw-tooth roofs, shown in 
Figure 63, would be expected to cause a circulation of air about 
as shown by the arrows. Moisture from the humidifiers will 
therefore be constantly carried up by the air current and depos- 
ited on the cooler windows and roof, not only rotting the wood- 
work but causing dripping. 

. The arrangement of heating coils shown in Figure 64 should 
reduce the air circulation by keeping the highest part of the 
roof at the highest temperature, thereby preventing the air 
from serving as a carrier of moisture from the humidifiers to 
the roof planks, and in so doing should reduce the rotting. 



68 



.^^ 




Fig. 63. 

Section of saw-tooth roof showing common location of heating pipes and 
air currents caused by them which deposit moisture ■ from humidifiers on 

the windows and roof. 




Fig. 64. 

A desirable arrangement of heating pipes located close to the ceiling and 

part of them near the top of the saw-tooth to keep the roof planks warm 

and dry, and prevent upward currents of moisture carrying air. 



69 

In paper mills and finishing works rotting can generally be 
stopped by increasing the ventilation, as the problem there is 
to get rid of moisture and thereby keep the roof below the dew- 
point. Where large quantities of moisture are to be disposed 
of a large amount of air will be required and provision should 
be made not only to remove this air but to admit and heat 
sufficient air to take its place without causing part of the 
circulation system to run backwards, a condition which is fre- 
quently found; that is, the exhaust ventilators, instead of carrying 
away the moisture-laden air, are admitting cold air in some 
parts of the room owing to a considerably higher temperature 
under the ventilators in another part. 

If fans are used and no provision made for introducing dry 
warm air in sufficient quantities to replace that removed, cold 
air will be drawn in about windows or doors and cause precipi- 
tation and rotting of the wood thus kept moist. An opening 
near the floor is advisable with suitable steam coils for warming 
the incoming air and of sufficient size to supply it in the required 
quantities to keep the air of the room at an absolute humidity 
of not over six grains of water per cubic foot. In a paper mill 
or finishing works, in which large amounts of water are evap- 
orated, this will require a large air supply. It may be possible to 
increase the economy of ventilation in such cases by returning 
some of the latent heat of evaporation of the outgoing moisture 
to the incoming air by use of an air condenser in the ventilators. 

Rotting in moist basements can more frequently be stopped 
by the introduction of sufficient radiated heat to keep the con- 
tained air above the dew-point than by ventilation which is 
commonly recommended. It is difficult to control the temper- 
ature of the air used for ventilation if it is taken from out of doors. 
The introduction of cold air into a warm moist basement will 
cause rotting rather than prevent it, as it will reduce the tempera- 
ture and precipitate moisture, while the introduction of a small 
amount of heat into such a basement will keep the temperature 
above the dew-point and thereby reduce the precipitation 
and tendency to rot. 

In several cases steam pipes near the ceiling of a basement 
have prevented rotting when the ground underneath was covered 
with water, as shown in Figure 65. The water being colder 
than the wooden ceiling assisted in keeping it dry by taking 
the water out of the air. 



70 




Fig. 65. 

Heating pipes on ceiling of basement over stream of water. Timbers still 
sound but other parts of this basement not so protected have rapidh' rotted. 



71 

SPECIAL HUMIDIFICATION OF COTTON FACTORIES. 

Humidity is an unquestioned necessity in cotton manufac- 
turing. If suitable study is given to its application it can be 
made to serve more acceptably in the manufacturing operations 
and at the same time not to menace the life of the building. 

There are two separate objects in introducing humidity into 
different processes of the cotton mill. In the carding and spinning 
it is used chiefly to prevent the accumulation of static electricity 
on the fiber which, if allowed to accumulate, would cause the 
cotton to draw unevenly, the individual fibers being repelled 
by each other, this not only causing breakage but fuzzy and 
uneven yarn. To accomplish this purpose a minimum relative 
humidity of 50% is sufiicient with a room temperature of 70°. 

This represents an absolute humidity of about four grains of 
moisture per cubic foot of air. It is probable that the removal of 
static electricity is more dependent on absolute than on relative 
humidity and that the minimum absolute humidity required is 
about four grains of water per cubic foot of air. On the other 
hand, if the relative humidity is allowed to get too high, an ex- 
cessive amount of moisture is absorbed by the cotton, and trouble 
from another cause is developed in the carding and spinning due 
to the cotton fibers becoming very soft and limp, causing the 
roving to pull apart, the common experience in "dog days." 
This will probably not give much trouble below 65% relative 
humidity. 

Mule spinning rooms are frequently maintained at about six 
grains of moisture per cubic foot, at which humidity rotting occurs 
if the room is at the top of the mill with the roof above exposed to 
winter temperature. The most of the carding and spinning rooms 
are not maintained at more than four grains of moisture per 
cubic foot. If sufficient moisture to rot the roof were introduced 
in a ring spinning room it would probably result in making the 
spinning run badly. Slasher rooms frequently give trouble 
from rotting roofs if they are at the top of the mill with a cold 
roof above. The remedy is to provide fans to carry away the 
steam from the drying yarn and an abundance of warm, dry air 
to replace that removed by the fans. This will not only reduce 
the trouble from rotting but increase the efficiency of the slashers. 

In saw-toothed roof weaving mills weaving fine yarns and 
maintaining 70% to 80% relative humidity trouble from rot is 



72 

practically universal. There is doubtless considerable difference 
in the humidity required by different goods. Stout, heavy 
warps with moderate twist will give little trouble at any reason- 
able range of humidity, while with fine warps high humidit}^ 
is a necessity. The stretch of the yarn upon which good weaving 
depends is increased by the humidity. 

Cotton comes into equilibrium with the relative not the ab- 
solute humidity, therefore if a room is maintained at an absolute 
humidit}' of six grains of water to the cubic foot throughout, one 
end of it being kept at 65° F. would be at goTc relative humidity 
and the other end being kept at 85° would be about 46^^ relative 
humidity, and cotton kept in the part of the room which is at 
65° F. would absorb about 13% of moisture, while that kept in 
the part of the room at 85° would absorb only about 6 % of 
moisture, although the absolute amount of moisture in the atmos- 
phere is constant throughout, that is, six grains per cubic foot. 

This suggests the practicability of regulating the humidity 
in a weaving room within limits at least by means of the tem- 
perature. B}' this means high humidities with equivalent 
moisture absorption could be used in parts of the room where 
required without discomfort to the help, and if at the same 
time the ceiling is kept considerably warmer than the floor, 
the danger of rotting will be much less than with high humidity 
at high temperature. In other words the high humidity required 
can be obtained b}' keeping the ceiling warm and the floor cool. 

The comfort of a weaving room is more dependent upon the 
temperature than the humidity. If the temperature is kept 
at 70° the humidity can be carried to 80% without discomfort. 
If, however, the temperature is allowed to rise to 80° the same 
relative humidity will be oppressive. A temperature of 70° 
would require an absolute humidity of a little over six grains of 
water to the cubic foot of air, to give a relative humidity of 
80%, which should meet the most exacting requirements of any 
kind of weaving. If the ceiling of this room is maintained at 
90°, the relative humidity which will be found here, and that 
with which the roof planks come into equilibrium, would be only 
a little over 40^ which will greatly reduce the possibility of 
rotting. 



73 

AVAILABLE LUMBER AND INSULATING MATERIALS. 

In making a double weave-shed roof the lower plank should be 
so chosen as to have suitable strength to support the roof and 
to be able to take paint well so as to maintain a good white 
reflecting surface. It should be of good heartwood of reason- 
able rot-resisting power, but if the insulation is properly designed 
should not require chemical treatment. Redwood, cypress, 
spruce or heart grade Southern pine should prove satisfactory. 
The lighter woods are preferable due to their better heat insu- 
lating properties. For the outer covering, lumber with thorough 
chemical treatment will be required. A vacuum and pressure 
treating process may be necessary to get thorough penetration 
if the lumber treated is thick or dense. There is no reason why 
chloride of zinc or sodium fluoride similarly applied by a vacuum 
and pressure process should not give satisfactory results. The 
objection to chloride of zinc, which should be given consideration 
in case of important structural supports, that is, its possible 
weakening of the wood, would have less significance for this 
use, as the strength of the wood is not so important. Low grade 
lumber can be used for this purpose. The more sapwood which 
it contains the better as the sapwood will absorb the chemicals 
more readily than the heartwood, therefore this use should 
make a profitable market for low-grade lumber and improve 
the higher grades by removing the temptation to mix in the 
lower grades. Lightness is a desirable quality^as the heat insu- 
lation roughly depends on the density. If water solutions of 
sodium fluoride, chloride of zinc or mercury are used the wood 
should be thoroughly dried before being placed on the roof. 
Hot creosote will probably be found most satisfactory for this use. 

No exact figures are available as to the thickness of insu- 
lating plank which will be required but it is probable that in 
the latitude of Massachusetts, with inside humidities of not over 
75%, 2 inches will be sufficient with about i Y2 inches of inside 
untreated plank and a one-inch air space. y% inch boards with 
a Y^ inch air space have been used in insulating an old roof, as 
previously explained. 

California redwood has recently been used in replacing a large 
roof in which the plank had been destroyed by rot. The light- 
ness and rot resistance of this wood recommends it and it should 
make an excellent material for roofs of moist factories. 



74 




Fig. 66. 

California redwood being put on a Xew Bedford weaving mill taking the 

place of Southern pine which had rotted in nine years. 



Fibrous or paper insulation such as hair felt, felt made of sea- 
weed or tarred paper in eight or ten thicknesses have been used 
with more or less success. When water-absorbent insulating ma- 
terials are used, great care must be taken to keep water and water 
vapor away from them, otherwise they will not only lose their in- 
sulating power on becoming wet but will encourage fungus by 
keeping the wood on which the}- rest continuousl}^ at the best 
moisture content for the fungus plants. 

Two roofs in w"hich rot was rapidh' progressing were insulated 
recenth' with seaweed, felt and "/%' creosoted lumber, the idea 
being to increase the heat insulation and raise the dew-point 
line above the old roof planks, thus stopping the progress of the 
fungus and saving the old roof with the minimum cost, and with- 
out interruption of manufacture. 



VARIETIES OF TIMBER AVAILABLE. 

The varieties of timber available for heavy mill construc- 
tion are fewer in number than those for structural purposes 
requiring smaller or shorter pieces. At present, the material 
in almost universal use for columns and beams in factories of 
"slow-burning '' type in the United States, east of the Rocky 
Mountains, is Southern pine. 



Occasionally hemlock or spruce is used for columns of the 
smaller sizes. In the older mills, columns of white pine and oak 
are often found. 

Spruce and hemlock are frequently used for floor and roof 
planking. Until recently, spruce plank was the favorite floor 
material for New England mills. 

Douglas fir is occasionally used for columns, beams and floor 
plank in the Middle West and will probably be more generally 
used in the future, as it can be had in good qualities and large 
sizes. The greatest manufacturing districts of the country are 
within convenient reach of the Southern pine forests, and Southern 
pine is undoubtedly used in much larger quantities than all 
other varieties, spruce plank being next, and hemlock, third. 
Therefore, careful study of the Southern pines is of the greatest 
importance. 

CHEAPNESS AS AN INDEX OF QUALITY. 

It is a significant fact that much of the best longleaf 
pine timber produced in the South has been shipped to 
Europe in the past. The European buyers consider quality 
first and are willing to pay a higher price for good timber. Too 
many of the American buyers of mill timber have been chiefly 
guided by price. Several lumber manufacturers, producing 
excellent longleaf pine timber, stated at the time of my visit 
in 191 5 that they hardly considered it worth while to quote on 
true longleaf timber to the American trade, as mixed varieties 
offered at a lower price, were practically certain to be accepted. 

COMMON VARIETIES OF SOUTHERN PINE. 

There is much confusion in local names. Mohr gives six 
Latin and twenty-nine common names as having been used 
at different times, or different places, for the longleaf pine, 
and the other varieties of pine have nearly as many. The 
Cuban and longleaf pines are confused, as both have long leaves, 
while the shortleaf and North Carolina both have shorter leaves. 

The positive identification of longleaf pine lumber is 
difficult or impossible. There are slight microscopic differ- 
ences in the form of the medullary rays of the North Carolina 
pine, as given by Penhallow ^ and Roth,- but to use them for 

1 " North American Gymnosperms," D. P. Penhallow, 1907. 
Bulletin No. 13, U. S. Division of Forestry, 1897. 



76 

identification would require considerable experience in the 
microscopic study of the pines. The microscopic differences 
are more striking with characteristic specimens. The longleaf 
pine is heavy, resinous and fine grained, averaging for the dry 
wood from the butt of the tree, according to Mohr, 36 lbs. per 
cubic foot. See Figures 68 and 72. 

The Cuban pine is slightly heavier, averaging -^^ lbs. per 
cubic foot, resinous and coarse grained, with a large proportion 
of dense summerwood, and a much larger proportion of sap- 
wood. 

The North Carolina pine, also known as loblolly pine and 
frequently sold as shortleaf pine, is lighter, averaging 31 lbs. 
per cubic foot, somewhat less resinous, coarse grained, with 
a large percentage of sap wood. See Figures 67 and 70. 

The shortleaf pine is the lightest of the four, averaging 30 
lbs. per cubic foot, the least resinous and of medium grain. 
See Figures 69 and 71. The tops of all varieties are generally 
lighter and less resinous than the butts. Cuban pine is never 
distinguished from longleaf in the lumber trade. The following 
photographs show the characteristics of the better qualities of 
the other three varieties, together with densities and rosin con- 
tents. 



77 




Fig. 67. 
Loblolly or North Carolina pine {Pinus taeda) . 

Rosin at A 14.6 %, B 1.6 %, C 3.1 %• 

Density at A 26.3, B 26.8, C 27.9 lbs. per cu. ft. 

A, heartwood; B and C, sapwood. 
Note the characteristic broad sapwood and dark grain bands, less clearly marked 
than those of the longleaf . 



78 



^M 



■■^■f 




Fig. 68. 
Longleaf pine log 29" in diameter {Pinus palustris). 

Note dark-colored, well-marked heartwood and comparatively thin sapwood, also 
fine grain bands with dark-colored summerwood. The resinous quality of the wood 
is indicated by the dark color. 



79 




Fig. 6g. 

Shortleaf pine {Pinus echinata). 

Rosin at A 23.3%, B5.2%, 04.4%, D 1.8%, £2.3%. 

Density at A 33.7, D 32.5, E 31. i lbs. per cu. ft. 
A, B, C, D, heartwood; E, sap wood. 

This wood is generally somewhat lighter in color, and less resinous in appearance 
than the longleaf. The dark summerwood in the grain bands is also not quite so 
clearly marked. 



80 




Fig. 70. 

Loblolly or North Carolina pine (Pinus taeda) . 

Rosin at B 1.9%, Density 26.5 lbs. per cu. ft., sapwood. 

f' Note the characteristic broad sapwood and dark grain bands, somewhat less 
clearly marked than those of the shortleaf. 



81 




Fig. 71. 

Shortleaf pine {Pinus echinata). 

Rosin at A 4.6%, B 1.6%, Density at A 30.6, B 29.1 lbs. per cu. ft. 

Note that the wood is generally somewhat lighter in color and less resinous in 
appearance than the longleaf. The dark summerwood in the grain bands is also not 
quite so clearly marked. 



82 




Fig. 72. 
Longleaf pine log 28" in diameter [Piniis palustris). 

Note the dark-colored, well-marked heartwood and the comparatively thin sap- 
wood, averaging about 2J4" in thickness. This timber, while undoubtedly longleaf 
pine, is inferior to that shown in Figure 42, as it is lighter in weight, less resinous and 
more subject to decaj', as shown by the fact that within a year after it was cut, 
rotting had started in the outer portions of the heartwood, although both sections 
were kept under identical conditions. 



83 

ROSIN AS A CAUSE OF RESISTANCE OF WOOD TO 

FUNGI. 

The causes of natural resistance to fungi in wood are obscure 
and have been investigated but little. Tannins in moderate 
concentration oppose the growth of Merulius lachrymans as 
shown by Wehmer.^ He finds, however, that they offer less 
hindrance to the Coiiiophora. The Daedalea qucrcina, on the 
other hand, thrives on tannin-rich woods; but this last-named 
fungus has not been found important as a destroyer of struc- 
tural timber, other than posts exposed to the weather. More- 
over, woods containing much tannin are now rarely used for 
mill construction. 
Heartwood is Generally Much More Resistant to Fungi 

than Sapwood. 

The process of heart formation in trees is little known. In 
the Southern pines it generally takes from twenty-five to fifty 
years and is frequently attended with increase in the rosin. 
In some of the oaks and locust, the tannin increases sharply 
at the line where the heartwood commences. The presence of 
starches and sugars in the sapwood, which serve as foods for 
fungi, as well as the greater water content of this part of the 
tree, is probably the chief cause of its more rapid destruction, 
while the resistance to water of the heart rosin and the anti- 
septic action of tannin are undoubtedly important factors in 
the resistance of the heartwood. 

The longleaf pine heartwood shows a wide variation in 
the rosin content, as can be seen from the several analyses 
given. It is evident that the top of the tree is generally less 
resinous than the butt, although this is not a universal rule. 
This would indicate that the only generalizations which can be 
made as to the durability of longleaf pine, as indexed by rosin, 
are that the average longleaf pine is more resinous than the 
average wood of the shortleaf and loblolly, and, in the longleaf 
heartwood, the resin is generally more uniformly distributed. 
The light nonresinous longleaf pine from the tops of trees, 
or from trees which have grown under unfavorable conditions, 
doubtless is no more resistant to decay than similar non- 
resinous shortleaf. 

The following statement is taken from a recent German 
work entitled "Hausschwammforschungen " (or House Fungus 
Investigation), Vol. HI, p. 178: 

1. Wehmer. Mycologisches Centralblatt, Vol. 1, 1912, pages 138 and 166. Vol. 2, 
page 331. 



84 

"All wood destroying fungi attack coarse grained Scotch fir 
sapwood more readih* than resin rich dense material. The 
Scotch fir heartwood under natural conditions is attacked \Aith 
great difficulty even by McruUus domesticus. particularly in 
small cultures. Resin rich knots are practically immune." 

The rosin, doubtless owes its antiseptic power chiefly 
to waterproofing qualities, preventing the progress of fungi 
by causing the wood to come into equilibrium with the average 
moisture of the air without sufficient water for their growth. Be- 
sides being present in the sapwoods of most of the pines in smaller 
quantities than in the heartwood. it is associated in the green 
sapwood with hygroscopic substances which annul its vrater- 
proofing action to a certain extent. 

Under the present system of grading and selection of 
Southern pine timber, the chief guarantee of durability 
is the proportion of heartwood. This is undoubtedly a 

sufficient guarantee for dry locations, if the timber itself has 
been well dried before it is put into the structure. Southern 
pine timber in a moist atmosphere cannot be depended 
upon, however, unless its durability is assured by a high 
percentage of rosin, or is reinforced by antiseptic treat- 
ment. In very moist locations a thorough antiseptic treatment 
is more reliable and can be obtained with greater uniformity 
than rosin. 

The percentage of rosin in the sound centers of rotted 
beams taken from a mill was determined in order to get 
an idea of the amount at which the fungus would not 
grow under ordinary mill conditions. See Figure 73. 

In the poorest of hard pine, there is generalh" a sound center to 
rotted beams, and this center contains more rosin than the 
remainder of the section. Sometimes it is not bounded by the 
growth rings but is very irregular, the cause being that rosin has 
been irregularly deposited in the section, o\\dng to knots or 
injuries to the tree. The limits of the sound center are not 
always the same as those of the heartwood. There is some- 
times a much greater deposit of rosin at the center of growth 
than in the older wood. In some of the shortleaf pines this 
peculiarity is conspicuous. See Figure 69. 

It is apparent that the limiting percentage of rosin at 
which the fungus stopped is in the neighborhood of three 
per cent. 



85 

The limiting power of rosin is undoubtedly not absolute, but 
varies with the moisture, variety of fungus, and time of exposure- 
Therefore, it is safe to assume that reliable Southern pine should 
have four or five per cent of rosin throughout. 

The rosin content is an index of the general good quality 
of the wood and as such can be used for comparing different lots 
of Southern pine. 

Both the rosin content and the density can be conveniently 
measured by boring one inch holes two inches deep into the end 
of the beam, collecting the chips, drying and weighing them, then 
extracting the rosin from them with benzol, and weighing it. 

The boring should be done with a bit, without a spur, which 
cuts a smooth hole with a flat bottom and can therefore be 
easily measured. A hole one inch in diameter and two inches deep 
will have a cubical content of .00091 cu. ft. 

The rosin extraction can be made most conveniently by 
means of carefully distilled benzol and a Soxhlet extraction 
apparatus. The drying can be accomplished in an oven main- 
tained at a temperature of 212° F. by hot water, electricity or 
other form of heat, and should be continued until the specimen 
no longer loses weight. A chemical balance which is sensitive 
to one milligram should be used in the weighing. The speci- 
mens should be kept, after being dried, until they are weighed 
in desiccators, with suitable drying agents such as strong sul- 
phuric acid or calcium chloride. 

Cuban or North Carolina pine with 10% of rosin is apparently 
as resistant to fungus as longleaf pine with the same percentage. 
Heart without rosin is not immune. 



86 




Re 


fttsA 12" s : : ' T 


:_f _ t^Jii5 


-^znoved after two 


yeais" service. 






B 


-^- 


~^-- "k 


-■^m 


B 




Ce&ter 
A 


C 




A 


Outer 
C 


tie 
7-72 


7-04 

4-89 

5-12 


.68, 

.76 

1.17 

-83 




20-21 
6.26 

3-45 
9-45 


12-17 
6.56 

2.31 


.88 
-58 
-99 
.82 



87 



DENSITY AS AN INDEX OF STRENGTH. 



The proportion between spring wood and summerwood 
is used as the basis of the " select structural " grade of 

Southern pine, and this is undoubtedly much in advance of 
earher grading methods, as timber containing much summer- 
wood is generally dense and strong. The proportion is difficult 
to determine with precision, however, particularly in material 
with fine or uneven grain. It is to be expected that a beam of 
irregularly distributed density will vary in strength, with the 
lighter wood located at the neutral axis, or at the part of maxi- 
mum stress. 

Weight per cubic foot of dry wood is a more accurate 
index of strength than the proportion of summerwood in the 
annual growth rings, which has been recommended as the best 
index of quality, and it can be obtained with greater precision. 

Light-weight wood is simply wood without much wood 
in it; in other words, all wood would weigh about 100 lbs. 
per cubic foot if it were solid. The difference between 
this and the actual weight gives the proportion of air 
spaces that it contains, as shown by the following photo- 
micrographs, made by the author, of transverse sections of 
Southern pine. See Figures 74, 75, 76, and 77. 




Fig. 74. 
Line between springwood and summerwood. Magnified about 15 diameters. 



Density has been shown by numerous tests of the United 
States Forest Service to be a reliable index of strength of 
timber. 

The proportionality between density and strength in the 
middle of its range (from 30 to 40 lbs.) with the longleaf pine, is 



88 




Fig. 75. 
' \'erj- light spring^'ood. ^Magnified about 400 diameters. 




Fig. 76. 
Moderately^light suminenvood. Magnified about 400 diameters. 




Fig. 77. 
Ven,' dense summerwood. Magnified about"40o diameters. 



89 

considerably obscured by other variables, such as season cracks, 
knots, cross grain, etc., as shown in tests given by the United 
States Forest Service.^ The range of density of shortleaf and 
loblolly is somewhat lower; therefore, only the best of these 
varieties will have a density above 30 lbs. per cu. ft. and 
most of the poorer longleaf pine will have a density below this 
amount. 

Photomicrographs made by the author, of transverse sec- 
tions of Southern pine of various densities, illustrate that density 
or weight per cubic foot is simply a measure of the amount of 
real wood present as distinct from air-filled cells. 

Johnson 2 gives the following rule: "Cross-breaking strength 
of all timbers, except the oaks, in pounds per square inch = 300 
times dry weight in pounds per cubic foot." 

The tests given by the Forest Service indicate that not much 
more than one-half of this amount can be depended upon with 
structural sizes of longleaf pine of average quality, the figures 
given being: 

Longleaf timber, green, 35 lbs. per cu. ft. dry weight, has a 
modulus of rupture of 6140. 

Longleaf timber, air seasoned, 39 lbs. per cu. ft. dry weight, 
has a modulus of rupture of 5691. 

Among the specimens from which these averages are taken, 
there is apparently only one below 32 lbs. per cu. ft. 

The moisture contained in wood is an important factor in 
its strength, as shown by many tests made by the United States 
Forest Service,^ longleaf pine and spruce increasing about 300% 
in strength as the moisture is reduced from 30% to o. 



Bulletin 108, "Tests of Structural Timber." 

2 J. B. Johnson, " Materials of Construction," 191 2, p. 680. 

3 Bulletin No. 70, " Effect of Moisture on the Strength and Stiffness of Wood." 



90 



SPECIFICATIONS FOR STRUCTURAL TIMBER. 



The selection and grading of timber is and probably always 
will be more or less of a gambling proposition. Grading rules 
can at best give only a general description of the qualities required 
with an attempt to define as clearly as possible the limiting 
acceptable characteristics. 

With lumber which is uniform, with only conspicuous defects 
such as spruce, the problem is somewhat simplified. With the 
Southern pines, of which there are several varieties so similar 
that they can only be distinguished with the greatest difficulty, 
it is much more complicated. In the past, botanical distinctions 
have formed part of all the specifications. Longleaf pine is well 
known to be the species that produces the best timber both in 
strength and resistance to fungus. Other varieties may produce 
as good timber but do not do so generally. 

The qualities which it is desired to guarantee by grading rules 
are strength and resistance to fungus. The strength is governed 
by the presence and location of knots, rotten wood, cross grain, 
etc., which are comparatively easy to see, and by the density 
of the wood which is less easily determined. The proportion of 
summerwood to springwood is the index of density made use of by 
the specifications adopted by the American Society for Testing 
Materials. 

The logical basis for a strength specification is the actual 
density of the material, which can be readily obtained by boring 
into the end of the sticks and weighing the chips. Under present 
market conditions such a specification while logical is probably 
impracticable, and the variations in strength must be taken 
care of as they have been in the past by a liberal factor of safety. 
A marked change has taken place in the lumber market since 
the publication of the second edition of this pamphlet in 1915. 
The price of all lumber has greatly increased and, due to trans- 
portation difficulties, as well as gradual reduction in the supply, it 
has become difficult to get lumber manufacturers to bid on 
carefully selected high-grade material such as that described in 
the previous edition as F. M. Southern pine. 

The general run of pine lumber used in mill construction, so 
far as I have observed it, has not greatly deteriorated. In fact, 
much less light sapp}' material is found in heavy construction now 
than was the case ten years ago, doubtless due to the general 
discussion and increased enlightenment on the desirable charac- 



91 

teristics of structural timber. At that time a considerable 
mystery was made of the grading and selection of timber, while 
now most of the buyers are better informed. 

Specifications are generally made by lumber dealers and 
describe what they have to sell rather than what the consumer 
wants to buy. Both buyer and seller must be considered, as it 
will be useless to write a specification describing something which 
is not obtainable or obtainable only in small quantities and from 
scattered locahties. The available supply at the time the pur- 
chase is to be made must also be considered, and the most prac- 
ticable material obtainable for the required purpose selected. If 
the moisture conditions are bad and material of high natural 
resistance to fungus cannot be obtained at a reasonable price, 
an antiseptic treatment which is practical for the purpose should 
be used. 

Durability. 

There is no absolute guarantee of immunity from rot in un- 
treated wood of any variety. Inside of heated buildings where 
there are no sources of artificial humidity, such as paper machines, 
drying cans, or cotton mill humidifiers, practically any kind of 
lumber will not rot if it is dry and sound when put in. Most of 
the cases in which serious rotting has occurred in such buildings 
has been soon after the building was built, and in the larger 
sticks in which the fungus was vigorously growing in the lumber 
yard before the lumber was put into the building. 

All sapwood is particularly subject to rapid fungus attack 
when filled with sap immediately after the tree is cut. Loblolly 
pine is one of the most troublesome varieties, not that it is more 
subject to fungus attack than sapwood or other varieties of pine, 
but from the fact that, due to its quick-growing habit, it generally 
has a much larger proportion of sapwood than other varieties. 
Light non-resinous heartwood of all varieties is also more sub- 
ject to attack than heartwood which is dense and resinous; 
therefore, when lumber containing much sapwood is used, it is 
practically certain to contain living fungus when received. 
Such lumber should be avoided in main supports of an important 
building unless thoroughly treated soon after cutting. 

The following are the specifications of the American Society 
for Testing Materials. 



92 

Standard Names for Structural Timbers. 

1. Southern Yellow Pine. — This term includes the species 
of 3^ellow pine growing in the Southern states from Virginia to 
Texas, that is, the pines hitherto known as longleaf pine {Pinus 
palustris), shortleaf pine {Finns echinata), loblolly pine (Finns 
taeda), Cuban pine {Finns heterophylla) and pond pine {Finns 
serotina) . 

Under this heading, two classes of timber are designated: 
(a) dense Southern yellow pine and (b) sound Southern yellow 
pine. It is understood that these two terms are descriptive of 
quality rather than of botanical species. 

(a) Dense Southern yellow pine shall show on either end an 
average of at least six annual rings per inch and at least one- 
third summerwood, or else the greater number of the rings 
shall show at least one-third summerwood, all as measured 
over the third, fourth, and fifth inches on a radial line from 
the pith. Wide-ringed material excluded by this rule will be 
acceptable, provided that the amount of summerwood as abov^e 
measured shall be at least one-half. 

The contrast in color between summerwood and springwood 
shall be sharp and the summerwood shall be dark in color except 
in pieces having considerably above the minimum requirement 
for summerwood. 

(b) Sound Southern yellow pine shall include pieces of Southern 
pine without any ring or summerwood requirement. 

2. Douglas Fir. — The term "Douglas Fir" is to cover the 
timber known likewise as yellow fir, red fir, Western fir, Wash- 
ington fir, Oregon or Puget Sound fir or pine, Northwest and 
West coast fir. 

3. Norwa}" Pine, to cover what is known also as "Red Pine." 

4. Hemlock, to cover Southern or Eastern hemlock; that is, 
hemlock from all States East of and including Minnesota. 

5. Western Hemlock, to cover hemlock from the Pacific 
coast. 

6. Spruce, to cover Eastern spruce; that is, the spruce timber 
coming from points East of and including Minnesota. 

7. Western Spruce, to cover the spruce timber from the 
Pacific coast. 

Many of the architects and large users of structural timber 
have specifications of their own frequently founded on the 1905 
grading rules which are as follows: 



1 



93 



THE INTERSTATE RULES FOR GRADING LUMBER. 

The Interstate Rules for Yellow Pine Lumber for 1905 
define "Prime Quality, Dimension Sizes," as follows: 

*'A11 square lumber shall show two-thirds heart on two sides, 
and not less than one-half heart on two other sides. Other sizes 
shall show two-thirds heart on face and show heart two-thirds 
of length on edges, excepting when the width exceeds the thick- 
ness by three inches or over, then it shall show heart on the edge 
for one-half the length." 

Merchantable Inspection. "All sizes under nine inches shall 
show some heart entire length on one side. Sizes nine inches 
and over shall show some heart the entire length on two opposite 
sides," etc. 

For chemical treatment sapwood is preferable to heartwood 
as it takes up the treating material more readily, therefore lob- 
lolly pine, which has a large percentage of sapwood, should be 
preferred. 




Fig. 78. 
F. M. Southern pine plank on a New Bedford saw-tooth roof. 



94 

The specification for F. M. pine based on density and rosin, 
which was recommended for structural lumber in the previous 
editions of this pamphlet, follow. It is now difficult if not 
impossible to secure bids on this grade of timber, but some of 
the finest Southern pine seen in New England in the past 
twent}^ years has been delivered under this specification. A roof 
of three-inch plank of this F. M. pine is shown in Figure 78. 
In ever}' case where this material has been specified the premium 
which it commands over common grades has been gladly paid 
and has been warranted b}' the quality of the goods. 



95 



SPECIFICATIONS. 

Suggested for a Special Grade of Longleaf Pine for Use 

in Mutual Factories. 

In making contracts for beams, columns and plank to be used 
in "Slow-Burning Construction," the following specifications 
are recommended for reasons given in the following pages. 

Density. No part of the material shall have a density of 
less than 30 lbs. per cubic foot when tested by boring smooth 
holes one inch in diameter and two inches deep in the ends of the 
stick, drying to constant weight at 212° F. and weighing the 
borings and computing the density from the volume of the hole. 

Rosin. None of the heartwood shall show less than four 
per cent of rosin by weight when borings are taken with a one- 
inch bit with a hole two inches deep, dried to constant weight 
at 212° F. and extracted with benzol, and the extracted rosin 
evaporated until it is neither soft nor sticky when touched with the 
finger at 70° F. 

Heartwood. Heartwood shall show the entire length in all 
four faces of every stick, and sapwood shall not extend more than 
two inches from the corner at any place, measured perpendic- 
ularly to the corner across the face. 

Growth Rings. For timbers 6" x 8", or larger, there must 
show on the cross section between the third and fourth inch, 
measured radially from the heart center or pith, not less than six 
annual rings of growth, a majority of which shall show at least 
one-third summerwood, which is the dark portion of the annual 
rings; but wide-ringed material excluded by this rule will be 
acceptable, providing that in the majority of the annual rings 
the dark ring is hard and in width equal to or greater than the 
adjacent light-colored ring. 

For pieces in which the center is not included, there must 
show on the cross section, an average of not less than six annual 
rings of growth, with not less than one-third summerwood. 
Timbers will be rejected in which there is no sharp contrast in 
color between the springwood and summerwood. 



96 

Defects. No timber with knots greater than one inch in 
diameter, or rot, or injurious shakes will be accepted. 

Branding. Longleaf pine sold under this specification shall 
be branded with the letters "F. M.," the name of the lumber 
manufacturer, the location of the saw-mill from which it comes, 
and the date of sawing, in letters at least one inch high. 

Douglas Fir. 

It will now doubtless be necessary to carefully consider Doug- 
las fir for structural purposes. It has many desirable qualities, 
but it has not become sufficiently common in the Eastern market 
to make its peculiarities familiar. While it is understood to be 
reasonably resistant to rot in the dry climate of the West, it 
doubtless cannot be used safely in moist factories without chemi- 
cal treatment. 

The most advisable procedure is to give it a superficial treat- 
ment with sodium fluoride as soon as it is cut to keep fungus 
out of it until it is in place in the structure. This may prove 
sufficient for the larger sizes. Planks for roofs of moist factories 
will doubtless require a second or a deeper treatment before 
being put into the building. 

Douglas fir is not quite so strong as the best grade of Southern 
pine, but it is more uniform and stiffer. It generally contains 
much less sapwood than the inferior grades of pine. In this it 
has the advantage over Southern pine, as this wood has the widest 
possible variation in quality. The best of it comprises the high- 
est grade of structural timber and the poorest represents the 
most unreliable of structural timber. 

The color of Douglas fir is yellowish brown somewhat re- 
sembling hemlock. 

Branding as a Guarantee. 

Many of the saw-mills are now branding their product with 
their names at least. Occasionally the grade and date are added. 
This is an excellent idea and should be encouraged, as it gives 
the lumber manufacturers an excellent motive for careful selec- 
tion. The following photograph. Figure 79, shows such branded 
lumber. 



97 




Fig. 79. 

The appearance of the standing trees of the principal varieties 
of Southern pine is quite characteristic, as shown in Figure 80 
but when these trees are cut into lumber it is difficult or im- 
possible to distinguish them. 




Longleaf 
pine 



Fig. 80. 

Shortleaf 

pine 



Loblolly 

pine 



98 

After the trees are cut into lumber, it is practically im- 
possible to check grades based upon botanical varieties. 

Branding, without a clearly defined description of the several 
grades, which can be checked by methods within the power of 
the purchaser, will depend for its value upon the honesty and 
carefulness of the lumber manufacturer; but, with well-defined 
physical and chemical specifications, such as those in common 
use with iron and concrete, the branding can be checked by 
the purchaser when necessary and will facilitate inspection on 
the job. 

True Conservation. 

Much is being written by students of forestry on the closer 
utilization of the forests. This is undoubtedly a commendable 
field of endeavor, but the utilization should be permanent 
and not consist in simply passing the loss along from 
the lumber manufacturer or dealer to the owner of the 
building. 

The use of timber, which, without antiseptic treatment, is not 
durable, in an important structure where it will rapidly rot and 
cause a loss of at least double its own value, is not proper utiliza- 
tion, since it soon results in economic waste of the most prodigal 
sort. Moreover, the careful separation of the lumber will in- 
crease the usefulness of the poorest. The sapwood, which is 
not safe to use in a moist place without antiseptic treatment, 
takes such treatment much better than heartwood, it being pos- 
sible to give some of the lightest and poorest of it a treatment of 
12 pounds of creosote to the cubic foot in an open tank, thus 
making it serviceable for use in moist locations. 



99 



CHEMICAL TREATMENTS TO PREVENT ROT. 

Antiseptic treatment is the only practicable procedure 
for lumber of doubtful durability, because of its porosity, 
light weight, sap or previous exposure to infection, or 
when it is to be used in a moist atmosphere. 

Much attention has been given to the treatment of railroad 
ties, posts, or other material intended for use near or in contact 
with the earth. But little study has in the past been given to 
the antiseptic treatment of factory timber. The well-known 
natural resistance of good longleaf pine in past years has been 
considered sufhcient to guarantee the permanence of structures. 
This is undoubtedly sound judgment when good quality, dense, 
resinous longleaf pine heartwood is used, as experience in the 
older mills has clearly shown, but the quality of pine now 
frequently used for heavy mill frames does not have this 
natural resistance. 

The use of this lower quality of timber, unsatisfac- 
tory though it be, has become a necessity. With antisep- 
tic treatment and reasonable allowance for the difference 
in strength between light-weight and dense timber, the 
quicker-growing varieties will fill the requirements of the 
future as satisfactorily as the longleaf Southern pine has 
done in the past; but the use of light, sappy, quick-growing 
varieties of pine, under conditions now found in many kinds of 
factories and other structures, without antiseptic treatment, 
has been and will continue to be followed by disaster. 

There is not yet experience enough with factory timbers to 
prove just how great an increase in life will be given by antiseptic 
treatment. Much depends on the exposure. Some idea may 
be had by the greater life of the dense "old-fashioned " Georgia 
pine as compared with some of the timber received to-day. 
Some idea also may be had from the increase of life given ties 
and telegraph poles by various processes, and by the experience 
with timber kyanized many years ago at Lowell and exposed 
under conditions that invited decay. 



100 

The increased life of railroad ties, due to antiseptic 
treatment, is given by Clyde H. Teesdale ^ of the United States 
Forest Products Laboratory, as follows: 

lo lbs. 1/^ lb. 

Untreated Creosote Zn. Chloride 

Years per Cubic Foot per Cubic Foot 
White oak 8 

Longleaf pine 7 20 

Douglas fir 6 15 11 

Spruce 6 14 11 

White pine 5 14 10 

Tamarack 5 15 11 • 

Hemlock 5 15 11 

The following table gives the increased life of telegraph poles 
in Germany and Austria, after being treated by several preserva- 
tive processes, as given by Dr. Frederick Moll,^ from Govern- 
ment records. 

Untreated poles 4.5 years 

Treated with zinc chloride 12.2 " 

Copper sulphate (Germany) 14.5 " 

Copper sulphate (Austria) 12.3 " 

Bichloride of mercury 16.5 " 

Creosote (15 lbs. cubic foot) 23.0 " 

What kind of antiseptic treatment shall be used is an 
important question. Numerous compounds have been pro- 
posed. The problem of treating timber for factory construction 
is different from that of railway ties and posts. Increased fire 
hazard, resistance to paint and a disagreeable odor are of no 
importance with ties or posts, but are of great importance with 
factory timber. Moreover, the leaching action of rain or ground 
water is important with posts and ties and of no importance in 
buildings where the material is protected from the weather. 
For this reason, the numerous creosote and tar compounds in 
extensive and successful use with ties are less suited to treating 
factory timber. Corrosive sublimate is preferable in locations 
where the moisture conditions are not unusually bad. In moist 
basements, in contact with the earth, or roof planks for moist 

1 American Lumberman, September 26, 1914. 

- American Wood Preservers Association, Proceedings 1914, p. 237. 



101 



weave sheds, bleacheries or paper mills, treatment with hot creo- 
sote with good penetration, preferably obtained by use of a 
vacuum, is advisable. The objectionable properties of creosote 
on ceilings can be compensated for by covering with fire- 
resisting sheathing, as previously explained. 

The fungus-destroying power of various antiseptics has 
been carefully studied by several investigators. The fol- 
lowing table is given by Falck.^ This not only gives the relative 
toxic power of the several materials, but the comparative value. 
The results are derived from laboratory experiments on ger- 
minating spores and fungus grown on various media. This must 
be given due consideration in estimating the practical value of 
the materials as preservatives. More reliable tests are those 
which are carried out over long periods of time under the con- 
ditions of actual service. Toxic materials may be either vol- 
atilized and removed, or chemically changed and thereby made 
inert, or they may combine with reactive parts of the wood and 
become inactive. 

By "inhibition concentration " is meant that strength which 
is just sufficient to destroy the fungus under investigation. 



Material 

Phenol 

Dinitro-o-cresolate of soda . 
2:4 dinitrophenolate of soda. 
Silicon magnesium fluoride . 

Sodium fluoride 

Boracic acid 

Corrosive sublimate . . . 
Sulphate of copper .... 

Chloride of zinc 

Sulphate of iron 

Salt 

As a result of his investigations of a large number of different 
proposed toxic materials, Falck recommends the sodium di- 
nitrophenolate, which is shown to be the most powerful fungus 
poison in the above list. This chemical is practically unknown 

^ Hausschwammforschungen, Vol. VI, p. 377. 



Inhibition 

Concentration. 

Parts in a 

Thousand 


Price per Pound 
Multiphed by 
Inhibition Con- 
centration 


I. 


SO 




05 


56 




05 


10 


I 




100 


I 




75 


2 




114 


I 




520 


10 




550 


5 




215 


20 




280 


100 




1000 



102 

in this country, and no experience with it as a wood preservative 
is available. Its chemical formula indicates a readily combus- 
tible substance, although it is stated that its explosive qualities 
have been overcome. 

Experiments made in the mines of France ^ with "Antinon- 
nine " showed it to be much less efficient than creosote as a wood 
preservative. This material is stated to be dinitrocresolate of 
potassium. From the chemical similarity, it would be expected 
that its action would not be much different from that of the 
dinitrophenolate and cresolate of soda given above. 

Sodium fluoride shows up very favorably in the above 

list. Its low price and high antiseptic value commend it. Ex- 
perience with it as a wood preserver is still lacking. Although 
a number of experiments have been started since the last edition 
of this pamphlet was published, but few results are 3'et available. 
Dean and Downs ^ give the toxic value of creosotes from 

laboratory tests as follows: 

Inhibition 

Concentration. 

Parts in a 

Thousand 

A Coal-tar creosote No. i below i 

B Coal-tar creosote No. 2 i 

C Water-gas tar creosote No. i 4 

D Water-gas tar creosote No. 2 3.5 

E Pressed anthracene oil above 8.5 

F Sample A minus the phenols 3 

G Sample A minus the phenols and tar bases 6 

Materials which are in no sense poisonous can resist fungus 
successfully, as in the case of the wood cells filled with water. 
It is probable that the beneficial result from some of the tars 
is caused by their waterproofing qualities. On the other hand, 
well-known bacterial antiseptics may be worse than useless for 
treating wood, as is shown by a building in Italy in which chlor- 
ide of lime was used on the timber.^ The chloride of calcium 
left in the wood cells attracted water and the building was quickly 
destroyed. 

1 "Preservation des Bois," E. Henry, 1907, p. 19. 

^ "Antiseptic Tests of Wood Preserving Oils," Dean & Downs, Journal of Indus- 
trial and Engineering Chemistry, Vol. V, p. 126, 1912. 

^ Atti del Reale Institute Veneto di Scienze Letters ed Atti, 1904, \'ol. XLIV, 
Parti I. 



103 



Goal-tar compounds are more used for preservative 
treatment of wood than all other materials together. 

They act mechanically and chemically, serving as waterproofers 
as well as antiseptics. There has been more or less controversy 
to the value of carbolic acid, naphthaline and other constituents.^ 

Most of the tar products used are by-products of the gas 
industry, and it is not a question of the most toxic material, but 
of the most toxic material with reasonable consideration of cost 
and permanence. 

Many proprietary compounds are being sold for timber 
treating. The price is generally high, ranging from fifty 
cents to a dollar a gallon. Coal-tar creosote can be bought for 
much less, and, judging from laboratory experiments of the 
U. S. Forest Service,^ as well as practical tests in the mines of 
France,^ creosote is fully as serviceable as an antiseptic where 
a coal-tar compound is required. 

The following figures are taken from a paper entitled " Tox- 
icity of Various Wood Preservatives " by C. J. Humphrey and 
Ruth M. Fleming of the U. S. Forest Products Laboratory: 



Killing Point in Parts per looo. 
Fomes Annosus Fomes Pinicola 



Wood tar (hard wood) 
Water, gas, tar creosote 
Coal tar, creosote . . 
Avenarius carbolineum 
S. P. F. carbolineum . 
C. A. wood preserver 
Sodium fluoride . . . 
Zinc chloride .... 



12.5 


7-5 


4.5 to 400 




5-5 


2.25 


52.5 


3.00 


22.5 




10 to 15 




2-5 


1-5 


5-0 


7-5 



It is apparent from these results that the toxic or killing 
power varies considerably with the variety of fungus. This is 
particularly marked with antiseptics of low toxic power, therefore 
the results of experiments showing moderate toxic power with 
a given fungus must be applied with caution to other fungi. 
Preservative materials of higher toxic power, such as chloride of 
zinc and sodium fluoride, show less marked variation with the 
different fungi. 

1 "Preservation of Timber," Bolton, 1885. 

"^ C. J. Humphrey and Ruth M. Fleming. Journal of Industrial and Engineering 
Chemistry, Vol. VI, p. 128, 1914. 

3 "Preservation des Bois," E. Henry, 1907. 



104 



The figures given on pages loi, 102 and 103 cannot be directl}' 
applied to the cost of timber-treating processes in terms of dol- 
lars per thousand feet. They show only the relative quantities 
of the several materials required to obtain the same poisoning 
effect on certain fungi. The second column of figures on page loi 
introduces the price per pound of the chemical in order to get 
a ratio of comparison; for example, if the corrosive sublimate 
required for a given penetration effect in an open-tank treating 
process costs two dollars per thousand feet of lumber, the same 
antiseptic effect could be obtained with sodium fluoride at a cost 
of about two dollars divided by 520 and multiplied by 75, that 
is. 30 cents. The labor would cost the same in each case. If 
instead of an open-tank process, a vacuum process is used, in 
which ten times as much solution is absorbed, the ratio still 
holds, that is, twenty dollars for corrosive sublimate and three 
dollars for sodium fluoride, although the toxic value pound for 
pound of the two chemicals is shown as the same, the dift'erence 
being due to the price per pound. 

Various observations show that Uquid oils do not thor- 
oughly waterproof wood, and, from all evidence obtainable, 
fungus is able to thrive about the same on oil-soaked wood as 
upon wood without oil, if the conditions of humidity are favor- 
able. An example of this is shown in the following photograph. 




Fig. 81. 

Rotted 3 " hemlock floor planks. Although saturated with paraffine lubricating 

oil, the fungus continued to advance where the moisture was sufficient. 



105 

which shows the under side of a piece of three-inch hemlock plank 
from the floor of a cordage factory, taken from under spinning ma- 
chines, where considerable quantities of moisture were being evap- 
orated, raising the relative humidity locally to near the saturation 
point. Strips of flooring about four feet wide, the entire length 
of the mill, were rotted under these machines, although this 
floor was thoroughly saturated with parafhne lubricating oil, 
so much so that the rotted wood removed dripped oil. 

It is evident that the moisture in wood is to a considerable 
degree independent of the oil which it contains. In other words, 
there is room for both oil and water under certain conditions. 
An example of this is wooden casks of linseed oil or varnish, 
which dry up and allow the contents to leak out, if not kept in 
an atmosphere of sufficient humidity to keep the staves swelled 
tight. It is probable that the liquid state of the oil has con- 
siderable to do with this action, and that resin or wax will prove 
more efficient as a waterproofing agent. For example, a part 
of this floor which had rotted was repaired several years ago 
with resinous longleaf pine. This is still sound. 

Coagulation of the albuminous compounds of the wood is 
frequently mentioned in the literature on wood preservation 
as an important factor. Confusion exists as to the difference 
between simple coagulation by boiling and combination with 
an antiseptic material. The former action could serve to ster- 
ilize already infected wood. This is one of the valuable results 
of kiln drying, but it in no way prevents later infection. A 
permanent combination of the antiseptic material with the wood 
can serve to prevent later infection. Bolton ^ is of the opinion 
that combinations between carbolic acid, or naphthaline, and 
wood albumen are of little importance, as the compound is 
easily broken up by water. He regards carbolic acid of little 
permanent value owing to its volatility. 

Creosoting, etc. 

The disagreeable odor, black, greasy surface and in- 
creased inflammability are objectionable qualities of the 
coal-tar antiseptics. In basement floors or rooms with wet 
occupanc.v, these objectionable qualities may not be important. 

An oily antiseptic in considerable quantity on exposed wooden 
ceilings can increase the fire hazard in sprinklered mills, as a 

* 1 "Preservation of Timber," Bolton, 1885. 



106 

fire once started can travel across the oil-soaked ceiling more 
rapidly than the sprinklers can open, involving large areas. The 
high flash point of the oil makes little difference, because a thin 
film on wood, which is a poor conductor of heat, is rapidl)^ heated 
by its own combustion to a sufficiently high temperature to burn 
rapidly. This action is decreased with time as the oil soaks 
deeper into the wood and the more volatile parts disappear. 
This action would be more serious in a building than in the open 
air where the heat would be rapidly carried away with the hot 
gases. 

Burnettizing by use of chloride of zinc is extensively 
used and has given generally satisfactory results for rail- 
road ties. It is understood to be considerably less expensive 
than creosote. There is, however, a suspicion that it may re- 
duce the strength of the material. The action may be slow 
but continuous and accelerated by moderately elevated tem- 
peratures. In a report on the preservation of timber by a special 
committee of the American Society of Civil Engineers in 1885, 
it was stated that burnettized bridge timber, that is, timber 
treated with chloride of zinc, was weakened 10% or more.^ It 
was also stated that railway ties treated with this material 
gave better satisfaction kept away from light and air by a cover- 
ing of earth. 

Chloride of zinc is a well-known solvent of cellulose. It is 
probable that if the timber was not deeply treated or kept at 
a moderate temperature it would do little harm. However, 
with deep penetration or higher temperature, investigation is 
needed as to its effect on the strength of the timber before it is 
recommended for indiscriminate use in the important parts of a 
structure. 

A series of tests extending over four years have recently been 
completed at the Massachusetts Institute of Technology. These 
tests indicate that if the treated timber is not raised in tem- 
perature above 100° F. the weakening is not very considerable 
or rapid, while at 150° F. the loss in strength amounted to about 
50% in a comparatively short time and was continuous. It is 
understood that the results of these tests are to be published in 
full in the proceedings of the American Wood Preserver's Asso- 
ciation for 1 92 1. 

1 Transaciions American Society of Civil Engineers, 1885, p. 325. * 



107 



Kyanizing. Kyanizing by use of corrosive sublimate was 
patented in England in 1832. Since then it has been in limited 
but successful use. 




I Tj-fi, nmmmdmim^imJLdMimmmasMmm 



Fig. 82. 

Kyanized spruce beam exposed to weather, with nails driven into the top 
of it, thereby opening cracks which admitted fungus through the thin area 

of treated wood. 



108 

The Locks & Canals Co.. which is the subsidiary corporation 
owning the water power and is in turn owned by the mills of 
Lowell, ]\Iass., commenced using this process in 1848 and have 
kept careful records of the results. For nearh" half a century 
this concern was under the actual management of one of the 
ablest engineers in America, ^Ir. James B. Francis, who adopted 
kyanizing after careful investigation and for more than sixty 3'ears 
maintained a small plant for treating such timber as was needed 
about the canals or in the mills in places peculiarly subject to 
decay. Spruce was the timber mostly treated. ^Slr. James 
Francis ^ stated that kyanized fence posts were in service in 1891 
that were set in 1850. It is understood that some of these posts 
are still in service sixty-three years after they were set. Timber 
parts of bridges, where conditions are exceptionalh' trying, re- 
mained in service thirty-two years. The bridge timber, how- 
ever, was carefully selected and seasoned before treatment, a 
condition which may have somewhat added to the efficienc}' of 
the antiseptic. 

The only failures of which I have been able to learn are base- 
ment floors where the planking was cut after being treated, 
thereby exposing the untreated center of the plank, for the 
penetration is commonly only about one-quarter of an 
inch. See Figure S2. 

Xails driven into kyanized timber exposed to the weather 
open cracks which admit fungus into the center of the stick 
beyond the effect of the kyanizing, see Figure 82. It is difficult 
to get deep penetration with the process either by heating or the 
vacuum and pressure process due to the fact that the mercur}' 
salt attacks all common metals so that about the only practicable 
procedure is to soak the lumber in concrete or wooden tanks 
for long periods of time. Sapwood is penetrated more com- 
pletely than heartwood. 

The method of treatment employed is to soak the material in a 
cold one per cent solution in a masonry, concrete, or wooden tank, 
the time of soaking being arbitrarily set at a day an inch plus 
one, that is, for a beam 4" x 10". five days, and for one 6" x lo",, 
seven days. ]\Iuch longer soaking is doubtless necessary if deep 



1 " Methods of Presen-ing Timber in Situations Which Expose It to Decay,'' 
Jan:es B. Francis. Xew England Cotton Manufacturers Association. Oct.. 1891. 



109 

penetration is required. It is claimed that the mercury once in 
the wood enters into chemical combinations with its albuminous 
constituents and becomes insoluble so that it cannot be leached 
out. 

The Berlin Mills Co., an old and favorably known concern, 
has a kyanizing plant and offers treated timber for sale. 

Several mills have recently treated roof planks with 
corrosive sublimate in their own yards. Wooden and con- 
crete tanks have been used. The concrete has proved most 
satisfactory from cost, tightness and convenience. The absorp- 
tion of solution varies from four or five to forty per cent of the 
weight of the timber, according to the amount of sapwood and 
fungus in the wood, and also the state of seasoning of the timber. 

Experience shows that the well-known poisonous character 
of corrosive sublimate when taken internalh^ by men or animals 
can readily be safeguarded, and, so far as T can learn, no sick- 
ness or death has ever resulted from the practical application 
of the process. In fact, corrosive sublimate in very weak solution 
is one of the most widely used antiseptics in hospitals and sick 
rooms. Only common-sense safeguards are needed, such as en- 
closing the tank and treating yard with a close fence, keeping the 
chemicals under lock and key and conspicuous "poison" labels 
attached to the tank. Preferably the treated lumber should be 
branded "kyanized" with hot, thin-edge iron letters an inch high. 

Kyanizing has no objectionable effect on paint subsequently 
applied. 

A Great Need for Better Data. 

On previous pages several preservatives have been listed, 
which promise well, but with most of them we lack experience 
on the practical application, their antiseptic power as well as 
their effect on the strength of the timber after ten or forty years, 
and as to their effect on paints, etc. 

There is now the same need for experiments on the natural 
resistance and the effect of various kinds of preservation upon 
full-sized beams and columns of commercially available timbers, 
under carefully controlled conditions of humidity and heat, 
and with exposure to known varieties of fungus, that existed 
a few years ago with reference to the strength of structural 
timber. 



no 

It is even less logical to generalize on the power of resistance 
to fungus of the several varieties of timber and upon the efficiency 
of timber treatments from laboratory experiments on small 
pieces in flasks, or small fungus pits where humidit}^ temperature, 
and fungus are not carefully controlled, than it is to calculate 
the strength of large beams from tests on small specimens. 

Moreover, experiments under practical service conditions do 
not give all the information desirable, for it has been shown 
that variations in atmospheric humidity, imperceptible without 
the use of carefuU}' arranged measuring instruments, are sufficient 
to account for the wide differences observed in the destruction 
caused by common wood-destroying fungi. 

The most practicable course is to get together as rapidly as 
possible data from actual experience in factories, and to make 
this information available for use of engineers as rapidly as 
it is obtained. The object of this pamphlet is to publish the 
information accumulated thus far so that engineers in designing 
mills need not repeat methods which have been shown to be 
inefficient, and further, to invite the co-operation of factor}- 
managers and engineers in the accumulation of this data. This 
co-operation will require a "clearing house " so that the in- 
formation will be available to all interested parties as soon as 
possible. Thus far the facilities oft'ered b}^ the Inspection Depart- 
ment for the accumulation and distribution of this information 
have made it particularly serviceable as a clearing house. 



Ill 



KYANIZING TIMBER IN THE MILL YARD. 



i I lis i ■ m 




Fig. S3. 
Southern pine heartwood roof planks for a paper mill, being treated in 
a shallow concrete tank, at a cost of about three dollars per thousand in- 
cluding the cost of the tank. 




Fig. 84. 

spruce planks and Southern pine beams for a weave-shed roof, being 
treated in a wooden tank. 




Fig. 85. 

2" Southern pine containing much sapwood, being treated for a weave-shed 
roof. Absorption varies from 5% to 35% of solution by weight. 



112 



A USE FOR CREOSOTED LUMBER IN INSULATING 
ROOFS OF MOIST FACTORIES. 

A new use for creosoted boards and planks is developing for 
the heat insulation of roofs of cotton-weaving mills and paper 
mills. The object is to stop the rot which is rapidly progressing 
in them by keeping the temperature above the dew point of 
the air in the room below. Two such roofs were installed two 
years ago in New England and are giving good results not only 
in stopping rot but in preventing sweating which has been trouble- 
some in cold weather. At present a Rhode Island weaving- 
mill roof is being covered with J^ North Carolina pine creosoted 
boards. This will require 130,000 feet of lumber which is being 
treated in an open tank in the mill yard. The concrete treating 
tank is shown in Figure 86. An absorption averaging six pounds 
per cubic foot is obtained, although some of the light boards 
are taking up twelve pounds. The following photograph, Figure 
87, shows several sections of the treated boards. The section 
at the top is exceptional. This is of dense Southern pine and 
has absorbed but little oil and shows slight penetration. The 
temperature of the oil exerts a greater influence on the penetration 
than the time of contact, very little penetration being obtained 
in twenty hours below the boiling point of water. At 220° F. an 
absorption of six pounds per cubic foot is obtained in twenty hours. 




Fig. 86. 

Treating %" boards for insulating a weave-shed roof with hot creosote in 

an open tank located in the mill yard. 



113 



Water in the wood seems to have little, if any bad effect, if the 
temperature of the oil is above the boiling point of water and 
the wood is kept in contact with the oil for twenty hours or more. 
In order to get some data on this point a piece of North Carolina 
sapwood was soaked in warm water over night with the re- 
sult that it was nearly water Jogged. This piece was then placed 
in the hot oil with a batch of lumber and took up twelve pounds 
per cubic foot over night. 




Fig. 87. 

Penetration obtained in an open tank with hot creosote on different kinds 
of Southern pine J^" boards. Average absorption, six lbs. per cubic ft. 



114 

PENETRATION OF ANTISEPTICS. 

The penetration of antiseptics has been increased by 
the use of vacuum and pressure processes, applied in closed 
tanks. Alternate heating and cooling also increases the penetra- 
tion. This process is sometimes carried out by dipping the 
timber first into a tank of hot material and then into cold, or 
by boiling it for a time and then allowing it to cool. By suit- 
able manipulation, in addition to obtaining considerable depth 
of penetration, the wood cells can be left full or nearly empty, 
as desired. This method is based on the expansion and contrac- 
tion of the air in the cells. A heating process might be used 
with corrosive sublimate to increase the penetration where 
this is necessary, special acid resisting tanks being designed. 
It is probable that the present method with the cold bath is 
sufficient for mill lumber not subject to excessive moisture. 

The relative penetration of the different common w^oods 
by oily antiseptics is given by C. H. Teesdale. ^ The depth 
of penetration is least with the first wood mentioned, and in- 
creases in the order given. 

1 Douglas fir heartwood 7 Loblolly pine heartwood 

2 White spruce heartwood 8 White spruce sapwood 

3 Eastern hemlock 9 Douglas fir sapwood 

4 Western hemlock 10 Longleaf pine sapwood 

5 Shortleaf pine heartwood 11 Shortleaf pine sapwood 

6 Longleaf pine heartwood 12 Loblolly pine sapwood 

Miss Gerry ^ shows that the tyloses, which are a sack-like 
formation in the wood cells, are a factor in the durability of 
woods as well as the penetration of antiseptics. This action is 
attributed to the obstruction which these growths offer to the 
advance of the fungus as well as to the penetration of air and 
water. Durable woods generally have tyloses, and they are 
especially effective in woods which have been dried. 

Brush treatments of timber with antiseptic solutions have 
some value in retarding the progress of fungus, as is shown by a 
recent Forest Service publication.^ A recent experience in 
a weave-shed basement shows that it is not safe to depend on 
brush treatment of timber already infected, if the antiseptic 
material depends chiefly for its preservative effect on its water- 
proofing qualities. 

1 Bulletin loi, Department of Agriculture, Forest Service, 1914. 

2 Journal of Agricultural Research, Vol. I, p. 462. 

3 U. S. Dept. of Agriculture, Forest Service Circular 198, Sept., 191 2. 



115 



COST OF TIMBER TREATING. 



The added cost of antiseptic treatment is not prohib- 
itive and it will become more necessary as good material 
becomes more scarce and expensive. 

It is necessary to see that the material is not water-soaked, 
frozen, or already deeply infected with living fungus when 
treated with cold solutions. The ideal time and place of treatment 
is immediately after sawing at the saw-mill, as much of the lum- 
ber is undoubtedly infected long before it reaches its final destina- 
tion. See Figure 88. 




Fig. 88. 

Fruiting lachrymans fungus on the frame of a lumber shed at a Southern 

saw-mill. 



A plan M^hich commends itself is to give the lumber a 
light treatment at the saw-mill with an antiseptic, such as sodium 
fluoride, which, being less poisonous than corrosive sublimate, 
would not prejudice it for common uses; then, after it is cut 
to final shape, to give it a second treatment suited to the condi- 
tions under which it is to be used. Indeed, corrosive subhmate 
applied in the small percentages required for timber preservation 
is very seldom objectionable. 



116 



SUMMARY. 



In conclusion, the following suggestions are made, based on 
observations and experience thus far: 

In building a paper mill or weaving mill, in which the atmos- 
pheric humidity will be high, antiseptic treatment is well 
worth its cost with any timbers now practicabl}' obtainable. 
A creosote treatment of about twelve pounds per cubic foot is 
as good as anything in practical use for moist locations where 
the fire hazard is negligible and the lumber is to be near or in 
contact with the earth, but concrete is general!}' preferable to 
timber in such locations. 

A form of construction for one story and basement paper 
mills and weave sheds which has many advantages, is a con- 
crete floor, protected steel columns, and a heavy plank roof. 
When a concrete roof is used in a cold climate and there is high 
inside humidities, it is necessary to provide efficient insulat- 
ing material on the outside to prevent the rapid conducting away 
of heat and consequent condensation. A dripping roof is highly 
objectionable for most occupancies. A thick wooden roof is 
the best heat insulator that can be had for the price. There 
are conditions under which it will be worth while, with this end 
in view, to increase the thickness of the roof to four or five inches. 
For securing durability in such thick roofs, it will be 
absolutely necessary to use material that is thoroughly 
fungus-proofed with suitable antiseptics. The roof should 
also be made sufficiently tight to prevent moisture-laden air 
from passing through cracks against the cold outer covering 
where the condensed moisture will keep the planks water-soaked. 

Thin plank roofs have been used in a few cases with fibrous 
insulating material on top, which can absorb water. The highly 
humidified air inside passed through cracks in the roof boards 
and saturated the insulating material with water, thereby de- 
stroying its insulating power and increasing the tendency to 
rot in the roof planks. 

For roof planks over rooms where humidity is high, chemical 
treatment is undoubtedly worth the cost. No experimental 
data is available as to the increased life to be expected from this 
treatment; but, judging from experience with other uses to 
which treated material has been put, the life should be greatly 
lengthened. 



117 

For use on a roof where insulation is the first consideration, 
the planks being made extra thick to secure this end, low-grade 
material can be used if it is made sufficiently resistant to rot; 
knots, shakes or resin pockets are of little importance if the 
material is thoroughly rot-proofed. 

For ordinary dry mills where the average humidity is 50% 
or less, Southern pine, spruce or redwood can be obtained with 
sufficient natural resistance to withstand fungus, untreated, 
if sufficient care is given to its selection. Heartwood in all vari- 
eties is necessary for durability. 



118 

The following suggestions for specifications are offered 
for use when Southern pine timber of an excellent quality 
is required. 

The following paragraphs will serve to eliminate much of the 
shortleaf, loblolh', and poorer qualities of longleaf, as well as 
to prevent misunderstandings and to facilitate the settlement 
of disputes if added to the specifications describing the required 
limitations of grain bands per inch and percentage of summer- 
wood, and the common limitations of knots, shakes, and wane. 
Under present market conditions it is practically impossible to 
obtain such material as described by the specifications. 

Specifications proposed. 

DENSITY. No part of the material shall have a den- 
sity of less than thirty pounds per cubic foot when tested 
by boring smooth holes one inch in diameter and two 
inches deep in the ends of the stick, drjdng to constant 
weight at 212° F. and weighing the borings and computing 
the density from the volume of the hole. 

ROSIN. None of the heartwood shall show less than 
four per cent of rosin by weight when borings are taken 
with a one-inch bit with a hole two inches deep, dried to 
constant weight at 212° F., and extracted with b inzol, 
and the extracted rosin evaporated until it is neither soft 
nor sticky when touched with the finger at 70° F. 

HEARTWOOD. Heartwood shall show the entire length 
in all four faces of every stick, and sapwood shall not 
extend more than two inches from the -^orner at any 
place, measured perpendicularly to the corner across the 
face. 

DEFECTS. No timber with knots, greater than one 
inch diameter, or rot or injurious shakes will be accepted. 

BRANDING. Longleaf pine sold under this specifica- 
tion shall be branded with the letters " F. M.," with the 
name of the lumber manufacturer, the location of the 



119 

saw-mill from which it comes, and the date of sawing, 
in letters at least one inch high. 

The above specifications will require selected longleaf pine 
from the butts of trees and will undoubtedly command a con- 
siderably higher price than "commerical longleaf pine." It will 
also be worth a higher price. It is a "grade " not known to 
the lumber trade at present. There is some of it in the South, 
but, by methods now in use, it is mixed with poorer timber and 
its good qualities are lost, as it is not the average, but the poor- 
est, that characterizes the lot. 

The place of shipment is no guarantee of the quality of 
the stock, as in most places where longleaf pine is growing 
there is also shortleaf and loblolly. 

In some places, the proportion of longleaf is greater than in 
others. The care and good reputation of the lumber manu- 
facturer is of more importance in assuring good material than 
the place of shipment. 

Branding the material with the name of the manufacturer 
encourages careful selection for its advertising value. 

Spruce and hemlock are undoubtedly less resistant to common 
timber-destroying fungi than good quality Southern pine heart- 
wood. 

New lumber frequently contains living fungi in a latent form 
which is difficult to detect. This difficulty is increased by the 
common practice at many lumber yards of planing the stock 
just before it is delivered. The only outward manifestation 
of fungus in the wood is frequently an inconspicuous brownish 
tinge. Nearly every lumber pile on careful examination will 
show a considerable proportion of fungus-infected sticks. In 
some cases these sticks contain tree fungi that are already dead 
and harmless. Living plants often start growing in the lumber 
pile, particularly if the weather is damp, showing lace-like growths 
between the sticks when the pile is taken down. Lumber show- 
ing such growths had best be given an antiseptic treatment, 
if the conditions under which it is to be used are at all moist. 

In several cases, serious rotting has been caused by timber 
which was water-soaked by being left uncovered during a long 



120 

season of rainy weather, and covered in without provision for 
drying. When it is necessary to use such water-soaked timber, 
it will be well worth while to hasten the drying as much as pos- 
sible by use of the heating system. 

Kyanizing can be conveniently done on the job by construct- 
ing a tank of concrete or plank of such shape that the material 
can be packed into it with the least possible voids. It should be 
weighted or held down with bolts so that it cannot float when 
the solution is added. This should consist of corrosive sub- 
limate dissolved in water, one pound to twelve gallons of water. 
The lumber should soak in this solution for a week. The absorp- 
tion will vary according to the quality and variety of the lumber 
from two or three per cent to forty per cent. Care must be 
used in handling the corrosive sublimate, as it is very poisonous 
if taken internally. 

Heat Treatment. 

When there is any suspicion of dry-rot infection in a 
new building, heating from time to time to 115° F., for a 
day or two by use of the steam-heating coils, is well worth 
its small cost for arresting the progress of a lachrymans or 
Coniophora infection. In a new building, it is particularly use- 
ful, as the heat not only arrests these fungi, but assists in drying 
the timber, and thereby kills other fungi. 

Drying . a moist basement will arrest many of the common 
fungi that require about ioo% atmospheric saturation. This 
can sometimes be accomplished better by a combination of heat 
and ventilation than by ventilation alone, as the heat reduces 
the percentage saturation where there is no water supply to 
keep it up by further evaporation. It is frequently difficult 
to get a circulation of air in a large basement without fans or 
other mechanical means. In some cases, air has been taken 
from a basement, which was giving trouble by rotting, for humidi- 
fying the mill, thus getting a return for the power required for 
driving the fan. 

In an infected building, the fungus spores would be so gen- 
erally distributed that the few brought up with the air currents 
would add little to the chance of infection of the upper parts 
of the building, which are drier, and therefore the possibility 
of the spread of the fungus from this source is remote. 



121 

One pound of corrosive sublimate dissolved in twelve gallons 
of wood alcohol has been used with apparent success on several 
occasions for local or surface fungus infections. In some cases, 
this material has been injected into small holes bored in large 
beams; and in others, it has been applied to the surface with 
whitewash brushes. 

The additional cost of the alcohol solvent is only worth while 
under exceptional circumstances, such as timber already in place 
in a moist location, or when economy of time is imperative. 
This method should be considered as an emergency measure and 
not for general application, due to its expense and doubtful 
efficiency. 

F. J. HOXIE. 



INDEX 

Page 

Abstract 2 

Antiseptics, Penetration of 114 

Antiseptic Treatment to Prevent Rot 99 

Arrangement of Heating Pipes 63 

Arresting of Fungi by Heating 69 

Branding, F. M. Specifications for Longleaf Pine 96 

Chamfering Upper Corners of Roof Supports Prevents Rotting 54 

Cheapness Index of Quality 75 

Chemical Treatment to Prevent Rot 99 

Chloride of Zinc Preservative 106 

Coal Tar Compound Treatment for Rot 103 

Coal Tar Preservatives, Odor Objectionable 105 

Combustibility of Wood Affected by Dry Rot 11 

Common Timber-Destroying Fungi 18 

Conditions Required for Growth of Fungi 39 

Conservation of Forests 98 

Construction, Slow-Burning 47 

Columns Used as Drains Start Rot - . . 61 

Cost of Timber Treating 115 

Creosoted Lumber for Roofs of Moist Factories 112 

Creosote Penetration, Open Tank 113 

Culture Block Showing Fungus 15 

Damp Rot and Dry Rot 32 

Data Needed, Regarding Experiences 109 

Defects, F. M. Specifications for Longleaf Pine 96 

Density an Index of Strength 87 

Density, F. M. Specifications for Longleaf Pine 95 

Design of Roof 50 

Destruction, Extent of, by Dry Rot 5 

Determining if Rot is Alive 14 

Distribution of Dry-Rot Disease 20 

Double Beams Do Not Prevent Rot 45 

Double Roof 55 

Dr3n.ng Arrests Growth of Fungi 30 

Dry Rot and Damp Rot 32 

Dry and Wet, Relative Terms 34 

123 



124 INDEX — Continued 

Page 

Examining an Infected Mill 12 

Experiences in Timber Treating no 

Exposure to ]\Ioisture Differs Locally 33 

Fire Hazard of Dry Rot g 

Forests, Conservation of 98 

Fungi, Names 18 

Fruiting Fungi, Identification of 20 

Fungi, Common Timber-Destroying 18 

Fungus, ]\Iicrograph of 22 

Grading Trees After Cut Into Lumber Impossible 98 

Growth of Fungi Arrested by Drying 30 

Guarantee of Durability is the Proportion of Heartwood . . 84 

Hammering Beams to Locate Rot 14 

Heat Treatment for Emergenc}^ 120 

Heat in Basement Prevents Rotting 69 

Heating Pipes, Arrangement of 63 

Heating to Arrest Fungi 16 

Heartwood, F. M. Specifications for Longleaf Pine 95 

Heartwood More Resistant to Fungi than Sapwood 83 

Holes in Columns Do Not Prevent Rot 45 

Humidification of Cotton Factories 71 

Humidity Affects Progress of Dry Rot 28 

Humidity, Average Relative of a Heated Building 28 

Humidity, Relative Desired 29 

Humidity Required in Certain IManufacturing Processes . . 34 

Identification of Fungi Sometimes Impossible 21 

Identification of Fruiting Fungi 20 

Identification of Longleaf Pine DifScult or Impossible .... 75 

Identification, Use of 20 

Identification of Location and Extent of Rot 13 

Infected Mill, Examined for Rot 12 

Insulating Material Available 73 

Insulation of Roof to Avoid Rot 30 

Insulated Roof, Section of 56 

Kyanizing by Use of Corrosive Sublimate 107 

Laminated Floors • . . . . 48 

Life of Dormant Fungi Long 39 



INDEX — Conimiied 125 

Page 

Limit of Dampness for Growth of Dry Rot 37 

Liquid Oils Do Not Waterproof Wood 104 

Loss from Dry Rot 5 

Loss, Roofs Greatest Source of 8 

Lumber Available 73 

Micrograph of Fungus 22 

Moist Exposure Differs Locally 33 

Names of Fungi 18 

Open Tank Treatment of Wood 112 

Paint Sometimes Retards and Sometimes Accelerates Rotting 38 

Penetration of Antiseptics 114 

Plank, Where Destroyed by Rot 53 

Prevention of Rot by Extreme Wetness and Dryness .... 36 

Progress of Dry Rot 27 

Progress, Recent 4 

Replacing Roof Plank no Guarantee of Permanency .... 59 

Reproduction of Dry-Rot Fungi 39 

Roof Design 50 

Roofs, Greatest Source of Loss 8 

Rosin, F. M. Specifications for Longleaf Pine 95 

Rosin Retards Growth of Fungi 83 

Rot Prevented by Chemical Treatment 99 

Rotting in Moist Basements 69 

Rules, Interstate, for Grading Lumber 93 

Saturation of Moisture in Cotton Mills . 37 

Saw-tooth Roofs, Location of Heating Pipes 68 

Slow-Burning Construction 47 

Sodium Chloride Treatment to Prevent Rot 102 

Source of Moisture for Dry Rot 37 

Southern Pine, Varieties of 75 

Specification of Antiseptic Treatment 118 

Specification for Special Grade of Longleaf Pine 95 

Specifications for Structural Timber 90 

Spreading of Dry-Rot Disease 42 

Steam Pipes, Location of. Under Saw-teeth 68 

Sterilizing by Heating System 42 

Structural Timber Specifications 90 



1 26 INDEX — Continued 

Page 

Structural Timber, Standard Names of 92 

Summary 116 

Test Holes for Examining for Rot 12 

Timbers Available 74 

Timber Treatment, Cost of 115 

Treatment to Prevent Rot , . 99 

Toxicity of Various Wood Preservatives ......... 103 

Ventilation Not Always a Cure for Rot .,.....,-.. 38 




THE ASSOCIATED FA 
FIRE INSURANCE 



LIBRftRY OF CONGRESS 

lihl II 



019 418 289 2 # 



I UAMUFACTURESS uuTUAL F. INS. CO. Providence, 

3 RHODE ISLAND MUTtTAi F. INS. CX)., Providence, 

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to MECHANICS MUTUAL F. INS. CO., Providence, 

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13 MERCHANTS MUTUAL F . INS. CO., Providcnce, 

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16 AMERICAN MUTUAL F. INS. CO., Providence, 

17 PHILADELPHIA MFRS. M. F. INS. CO., Philadelphia, 

18 RUBBER MFRS. MUTUAL INS. CO., BostOn, 

19 PAPER MILL MUTUAL INS. CO., BostOn, 

ao PROTECTION MUTUAL F. INS. CO., Chicago, 

Revised, Feb. 1922 



JOHN R. FREEMAN, PtCS. 
JOHN R. FREEMAN, PtCS. 

J. P. GRAY, Pres. 
F. w. MOSES, Pres. 

JOHN R. FREEMAN, PtcS. 

w. E. BUCK, Pres. 
E. V. FRENCH, Pres. 
WM. B. McBEE, PlCS. 

C. s. WARING, Pres. 

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c. c. STOVEB, Pres. 

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c. c. STOVEB, Pres. 

BENJ. TAFT, SeC. 

JOHN R. FREEMAN, PreS. 

£. I. ATLEE, Pres. 

BENJ. TAFT, SeC. 

D. w. LANE, Pres. 

J. L. WILDS, ^ce-Pres. 



The Factory Mutual Fire Insurance Companies were originated 
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